It seems the Government would like to introduce ISA accounts for children sometime next year. While there's little detail yet, This will likely give the option to save in stocks & shares or cash, just like conventional ISAs.
Given the Government won't be putting any money into the pot, Junior ISAs are hardly anything to get excited about, but being tax-free they could make tax affairs simpler when saving for child compared to the present.
At the moment savings and investments are only taxed as a child's if held directly by them or via a bare trust. Otherwise parents, grandparents and other relatives could find themselves liable for tax on income and gains. And parents are liable to income tax on annual income that exceeds £100 per child per parent on money they've gifted.
Given most people seem to be ignorant re: these tax rules (hence probably don't pay tax) I doubt the introduction of a Junior ISA will cost the Treasury much money. But it will only stand a chance of working if a sufficient number of ISA providers offer accounts to ensure decent competition and choice.