Cyrpto is pretty volatile for a long-term investment and the current thinking is once the market stabilizes and there is a recognized and accepted defacto Blockchain tech that receives widespread adoption that it will cause the floor to basically drop overnight on most coins.
Why not instead open a Roth IRA and add funds to it once your children begin earning any type of income? This could be from mowing grass, babysitting, or other fractional summer work. You can add to their IRA up to what they earn if it is less than $6000 and your children will be able to draw on it for college, pay for their first house, or enjoy the benefit of accessing it tax free once they reach 59.5. $6000 compounding for 40 or more years in a decent mutual fund with lifetime average returns at or above 10% is a good chunk of change. https://www.fidelity.com/retirement-ira/roth-ira-kids