Well done for letting them stay. They can be quite interesting to watch and as you have found, can be good with keeping other bugs, including spiders, away.
I'm not sure of the weather where you are or how often they have been breeding but often a wondering spider (like the one you have) would be a male looking for a mate. I can't quite see the pedipalps in the photo, which would be a way to sex it, but the body shape suggests a mature male.
Males don't live very long so try and mate when they can. Some species do wonder but not so much Steatoda which tend to sit by their web. If you have lots of young too, it could be time for the male to try his luck again. There is also a very good chance that the numbers of young you have will diminish as they are cannibalistic and will eat each other.
Most spiders, especially in the UK, don't tend to bite. Only a few can penetrate human skin. This often depends on the size of the spider so most spiderlings probably couldn’t bite even if they were provoked. All spiders have venom, though the strength can vary a great deal. I have read that false widows do have a painful nip, but I've never been bitten. I've never seen some aggressive or attempted to bite either, and I have breed some. If poked or prodded it could bite though.
My advice would be to maybe move the male somewhere else, with a glass jar and some paper. It would be better if he could mate with a different female anyway and would help with any concerns you or your girlfriend has with your son. As long as you release him somewhere quiet and not too cold he will be ok. Keep an eye on the numbers of spiderlings, they tend to move away from each other with time but if you feel the numbers are getting out of had just move some on the same way.
You should be able to enjoy them without worry and my little lad has grown up to respect bugs from a safe distance but get quite a lot from watching them.
