While Goldbacks are fun to collect, I think smaller denomination silver coins in your country's official currency are best since they're easily recognizable.
I do a little bit of it all. I have collector pieces that appreciate in value as an investment for the future. I have low-premium rounds, coins, and bars if I need to sell. The goal is to not have to sell and leave it to my boys as part of their inheritance.
I can still remember the first coin I bought as a kid. It was a Morgan silver dollar from 1890-something, I think. I sold it two years later to make my first bank deposit (it had increased in value since then). I like that you're saving for your kids, and a balanced approach might also allow me to toss some into a bug out bag just in case. No power, means no ATM to get cash from, so its good to be prepared.
There you go. Don't forget gold, too. While I stack silver, I doubt I'll take it with me in a bugout situation. For that, I have a bug out case full of gold.