My 5 year old adores science, and together we play about with the usual kitchen science..
Vinegar and bicarb in various guises to fizz and pop..
Washing liquid in milk etc
I've got a few books on order, but would love to hear what experiments you remember from school, our do with your kids!
It would be cool if it was all easily accessible chemicals, but might hunt about online for other bits and bobs!
DrP
paperclips in a plasticine boat is a good one, as well as soap boats (surface tension)
paper aeroplane building is another that can whittle away hours
Diet Coke and Mentos (but outside)
water and oil shake and wait [ immiscible] then add washing up liquid.
There is a good you tube channel on kids science
will search it out for you
When I was 11 my dad brought home a dead rat for me to dissect 😯
That's probably not the sort of thing you're looking for though . . .
Non newtonian fluid..... Cornflower and a little water... Stir it slowly and it's wet, fast and its hard (oo Er) can be poured onto a board and hit with a spoon/ladle/ mallet and won't splash... Add a bit of food colour for added effect. Easy to clean up!
dish of water with a candle in it and a jam jar stood over it,
pulls the water up from memory.
Cartesian divers.... [url= http://www.physics.org/tricks/cartesian-diver/ ]linky....[/url]
Ha Esme, that reminds me when I was a kid my Dad brought a flask of liquid nitrogen home (he was a physicist) and we dipped things in it and threw them against a wall to watch them shatter! Carrots, bananas and the hose pipe spring to mind!
I guess an eighth and aunt Bessie's brownie mix isn't what your after? 😉 😉
What daftvader said, non-newtonian fluids are great fun for kids (and adults).
marshmallows on a tray and a microwave (above the turntable), lets you calculate the speed of light.
( http://www.physics.umd.edu/icpe/newsletters/n34/marshmal.htm )
Work out Planks Constant with Lego (my project for the summer!)
[url= http://arxiv.org/abs/1412.1699 ]Lego Watt balance[/url]
Youtube is packed with stuff for you - go look up something like a water bottle rocket and go from there...
Cleaning coins with various bits and pieces like brown sauce, vinegar, coke etc.
Take a plastic jug and fill it with gravel. Shake and wobble it. It's full, right?
Then add sand, shake it and wobble it until it's full. No more room see, it's full, right?
Then add beer.
Result: there is always room for beer.
Pen top submarine.
Candle is a bowl of water upturned jarover the top and watch the jar fill.
Bottle rocket!
If you do the candle in the upturned jar, just don't tell them the water's risen up because the flame used all the oxygen... very persistent wrong explanation!
[url= http://www.itsjustabox.com/Sciencefair.htm ]Chromatography[/url] with black felt tip pens is fun
Explode custard powder in a syrup tin. Will need supervision.
You need
Syrup tin
a tealight
some tube
a wee squeezy plastic bottle.
Do it outdoors. Can upgrade to catering coffee tin if you get good.
DIY T-shirts
You need:
Photocopied image (keep it simple)
Plain T-shirt
White spirit, water and washing up liquid, old bottle of some sort
Baking tray big enough to fit the photocopy in
Iron, ironing board, plastic sheet & old tea towels
White spirit and water in the bottle (can't remember the ratio so try 1:1) and add a drop of washing up liquid. Put lid on and carefully shake to mix.
Put photocopy into tray and pour over mixture
Plastic sheet on ironing board to protect it and lay T-shirt on with side you want the image on facing up.
Remove wet photocopy from the tray and lay on the shirt
Place a tea towel over the photocopy and iron
Image should transfer from the photocopy to the T-shirt.
Bingo - DIY T-shirts using nothing more than stuff you find at home. Might also work for colour printing and laser printing but never tried that when I was a kid.
purify DNA from kiwi fruit or buy some magic sand
Non-Newtonian fluid is a good one:
Build your own [url= http://en.wikipedia.org/wiki/David_Hahn ]Nuclear Reactor[/url]
Potassium permanganate
Sugar
Glycerine
Available from your local pharmacy 🙂
Another one... But potentially very messy... Photocopier toner and water in a petri dish, magnet underneath... Pretty patterns.
Extracting iron from breakfast cereal is a good one ...
daftvader - and not something I'd advise near kids, toner isn't very good for you if inhaled.
Get some cheap kitchen scales and get some varying weights between 1g and 500g.
Force them to weigh each weight a bazillion times, noting the results given in a lab book. Then force them to carry a statistical test to see if any of the scales differ significantly from one another. Then force them to write it all up and consider why variation in instrumentation is important, making sure they harvard reference. Tell them their pocket (grant) money is dependent on you receiving adequate results. Halfway through.... break 2 of the scales and force them to fix the scales as you cannot afford to buy anymore. Tell them to consider the effects of this on their experiment, also admonish them for not maintaining the cheap and nasty scales in the first place. Make them wear gloves, goggles and face masks into the play room to carry out their experiments. If they do not, note it down and bring it up in a performance review. After they have given you good results, tell them they are fired and will no longer be entitled to any pocket money other than what they are owed.
......science. 
......maybe when they are 10 😈
...............I'm going to be an awesome dad.
Iodine crystals. Soak with ammonia. Leave to dry. Hit with a hammer.
Then next time do it outside because the explosion stained everything in the room purple 😉
My dad is a chemistry professor, though, so I probably had access to stuff that's not so readily available...
Actually a lot of cooking can be linked to science, particularly chemistry. We do a lot of biology when I joint meat, or fillet a fish. Some of the morphology in a chicken is great for explaining dinosaurs, and saving and using ligament from a deer makes superb bow.
On a less controversial note balancing a needle on water (surface tension) to show how a compass works.
You can make graphene in your kitchen using a couple of trivial methods. Trouble is, there's no obvious endpoint for the experiment (AFAIK) that could engage children, you'd just be pointing at a load of black shite and calling it graphene.
Might be worth it for older kids, peeling it off with scotchtape to show how simple experiments can lead to a Nobel prize.
[i]Ha Esme, that reminds me when I was a kid my Dad brought a flask of liquid nitrogen home (he was a physicist) and [/i]
I had an interest in biology and anatomy when growing up. My mum was a theatre nurse...
If anyone is still interested, there's an article in the latest New Scientist mag.
Flash freezing water (spectacular... If you get it to work)
[url= http://www.stevespanglerscience.com/lab/experiments/cloud-in-a-bottle-experiment ]Clouds in a bottle[/url]
Testing stuff with pH paper - my classes love this.
As mentioned before - non newtonian fluids are great.
Anatomy can be done with a whole fish/crab/lobster from the fishmonger.
Pepper sprinkled onto plate of water then touch the surface with a finger covered in washing up liquid.
Did a science party for my 5yr old lad. He loved it. Used a few of these: [url= http://www.whynotchemeng.com/teachers/top-ten-flash-bang-demos.aspx#.VPIK4EeQGrU ]http://www.whynotchemeng.com/teachers/top-ten-flash-bang-demos.aspx#.VPIK4EeQGrU[/url]
Also, check out a guy on YouTube called the crazy Russian. He has got all the science based tricks you need to keep your lad entertained for months!
The methane bubbles / light in your hand one always gets them.
For the boys party I managed to get some 35% hydrogen peroxide and potassium iodate solution for a volcano experiment. Made a massive paper mash' volcano. Doubled the volumes I was previously working with and covered the ceiling in the hall I was doing it in with foam. kids loved it.