Making an investment on behalf of my child

[Windyone]

I wonder if there is anyone around who has been in this situation who can give me advice.
My son has inherited a decent sum of money. I have to administer it until he is 16, he is currently 13. I need to find a savings account or bond that I can either open in his name or jointly. Most banks have a savings account for children but the rates of interest on those accounts are dreadful.
I'd be very grateful for suggestions for other products?

Had a similar situation for my child.
We looked at/used the following for the cash savings :

Nationwide Smart Limited Access 2.25% up to £50,000
Halifax Junior ISA 3% (if parent has account) up to annual amount of £4,128

That's about the best you'll find at the moment for cash accounts. If he's likely to keep it saved until he's at least 18 wouldn't it be worth looking at some sort of stock market investment?
What sort of sum are you looking at?

How much are we talking?.... anything over 50k I'd take some advice.