Is this a thing? He is only 13 - can he invest it himself or would I need to do it for him? And I mean really small amounts, I would guess under £50. I think he just wants to see how it works and if he can get any return from it.
If it's not possible, are there other ways I can support his interest in finances? He doesn't have a job - his only money is from birthdays and doing jobs around the house. He is very good at maths and has a growing interest in economics and all things money-ish.