Saving bitcoin for your children's future is a fantastic concept, but given the volatility of bitcoin, it will be challenging for parents to hold onto their investments over the long term without being driven to sell when the price is falling or rising.
You can't save without using wisdom, thus if you want to use bitcoin to save for your kids' future, you must do it wisely. Suppose you bought bitcoin when it was inexpensive for your children and sold it back when it was expensive (4 years invested plan of the bearish market and the bull run).
Being responsible towards the unpredictable future of bitcoin, I agree with you. If parents have the opportunity to make a safer investment, while maintaining its profitability against fiat devaluation, they should go for it, instead of bitcoin investment.
The issue is that most people don't have a large chunk of money to make such investments, so they are left with the alternatives banks give them, like saving and fixed income accounts. In my opinion none of these are alternatives thinking on the future of children, due to their low interest rates, therefore bitcoin is still a very viable option for our money, because there are good chances it will be much more valuable in a decade or so, besides being possible to invest any sum of money anytime, without any barriers.
To set a number, at least 10% of our childrens' savings should be invested in bitcoin, being very conservative.