You have a junior ISA which locks up the money until they are 18 but then they have full control over it. Normal ISA rules for tax.
You can put money into a SIPP for them which will lock it up until they are 57!
Between those there is no easy access mainstream account like the above (I think). One option is to open up an account in your own name and save there, especially if you aren't using all of your ISA allowance each year currently. Then you can pass onto them either in a lump sum or parts when you see fit.