You have a few options that all have pros and cons.
To retain control you should save in your name.
Why would you need control? There are hundreds of posts on MN about teens wasting ££££ that they received (savings/inheritance/windfall etc). How should you save for 10+years? I would suggest a S&S ISA.
You could then withdraw the appropriate £ when the time comes.
Saving in the child's name?
Traditional bank/building society = safest but currently very low interest rates. With the way the economy is going with world events then rates may well rise but inflation could also spiral.
Child S&S ISA = volatile at present (world events) but likely to grow the best in the long term.
Pension = very long term savings option where they only gain access age 57.
Ideally you could do a mix of all of the above but as there is only so much £££ in the pot then do your research (there's another thread about financial literacy on the go the last few days) and pick whatever suits your circumstances best.
FYI I use Vanguard at present for pension and S&S ISAs having used traditional banks when they were younger. If I had my time again then I would have started the pension from birth and likewise the S&S ISAs. Vanguard is one of many providers ie more research for you.