I've got stocks & shares ISAs in the name of each of my children. The return has been a lot higher than if I'd put their money in a cash ISA.
I've also been putting the equivalent of the child allowance (£84 pcm) into SIPPs for them since birth. The government also kindly adds something (20% iirc). My daughter is 17 years old and she's built up about £48k in her SIPP. I know they won't be able to access this until they're aged 55 (under current legislation) but it's a good start for them