This any good?

Budget 152mm triple
Edit: my daughter has a Scott 24″ wheeler (Voltage?) and it has a triple, she never gets in the big ring either

Islabikes spec’ed 1×7 SRAM with gripshift. Seems to work OK. Losing the second ring at the front also saves on shifters and cables so it can add up.

Next up service the hubs, bottom bracket, derailier etc. Get all the friction out of the system. Then fettle the brakes and gears to make sure there’s no drag. It can add up when you’re small.

Consider tyre choice and rolling resistance. If they don’t go out in deep mud, then get some summer slick on there. Play with tyre pressures while you’re at it – low pressure for you is probably high pressure for your children. My son has 2″ tyres and runs fatbike pressures.

For a kid that age I wouldn’t bother with a triple. The front / rear thing means there’s just too much going on. 1 x n would be the best setup IME.Ideally something like a 28 on the front, though if its just 28 at the rear I’d maybe go even lower.

There are a few cheap 150 chainsets out there, though my son struggled with the hills where we live until he got a low enough gear. He still tends to spin out in the little ring but does use the middle as well now.

Light, easy rolling tyres would be a good upgrade.

My son also gets on a lot better with trigger shifters than he did with gripshift.

I got my son a scott voltage 20″ for xmas and totally stripped it, got rid of the triple chainset and put on a funn hooka single ring 34t set up with superstar chain device, continental explorer tyres, hope 50mm stem, easton carbon bars,sdg i beam post with i sky jump bike saddle, lightend it up loads, most of the parts sorted from the forums

i put 145mm ones on £29 from crc

Lots of good advice, also look at the cassette you can get some screw ons with a 36t bail out gear.
Bars and stems and seat posts are worth looking at, they are often steel or lumpy alloy. I’ve fitted used flat bars in the past. You can pick very light stuff keep. But even new lower gear is a lot lighter than whats fitted.

Not sure if I am really wrong here, but at 8 maybe just move him up a wheel size? Really helped my kids, especially on climbs. Rolls better, much more confidence. Unless your 8 year old is reall short, I should easily fit. Most 24″ wheeled bikes have very small frames.

My own 8 year old is the size of his 11 year old brother and has outgrown his 24″ bike and now has a 26″ bike with tiny frame. Old rockhopper frame built with light parts of the forum, he loves it and has really improved. He also stopped complaining his back hurts since moving up ( must be a size thing as he went from a spesh full suss to a hardtail ).

I’d say consider moving up instead of spending money on the 20″ bike. Just a thought….

Maybe it’s just my youngest that grows like a weed! He is 4″7 ish now, or was that yesterday…

Still his 24″ spesh frs was getting too small in summer when we sold it. They do only have 12″ frames mind you, the 13.5″ spesh hardtail would have still fitted him. It seems to be all about the frame and standover height. My kids ( oldest is 11 ) also have a norco b line 24″ bike, wich still fits them easily as the frame comes up really big.

They seem to be most comfy on bigger wheels, small frame, short stem and cranks. This also gives them growing room. Small light frames with short reach are hard to come by though in 26″.

Still, i did not consider my kids big enough for 26″ wheels till they tried them in tiny frames, they loved them. My friend got them to give it a go. When we owned a 26″ for my oldest and a 24″ for my youngest, my little one prefered the 26″ and would always choose that when asked.

We ended up hardly using the 24″ bikes as we kept them on the 20″ hotrock for as long as poss. They really shoot up at this age! I sometimes teach 10 or 11 year olds that are my height at 5″4.

Good luck!