You will need their ss numbers. They can’t touch it till they are 18. At that point they can take the money out and spend it anyway they like. If you take money out of the account they’ll be a tax consequence. You can trade it and have no consequence tax wise.
I went a slightly different route. I have a set amount of shares set aside within my ROTH to assist my grandchildren with their education. This is not identified through E*Trade, or any government program. Simply a budget within the ROTH for their use when at college age. For me, the beauty is that I am over 59-1/2 and can withdraw tax free and without penalty at any time. If I pass, they will inherit the funds through the ROTH, tax free.