Well it's not just stablecoins, but everything about crypto itself. There's just many to cover first before making your kids use any forms of crypto out there. The security, the risk, the methodologies, and the technical stuffs that they need to obtain first before keeping their hard-earned money into crypto.
Kids should not touch money too early as they can lose control and get distracted to many things in life. As kids, they must learn, focus on education and some soft skills that can be helpful for their life, interactions with other people. Money is not main thing and priority for kids when you are as parents want to educate them.
Cryptocurrency or Bitcoin can be taught to kids through funny games and I remembered there are some such games designed specifically for kids.
I don't think every parents out there are going to consider this though. It is each of their own at this case. There are parents that do not fancy tech stuff involving their money. My parents aren't really a fan of credit card and I was not able to use it til this day as I don't want to be in debt.
Each generation will be exposed to one or some big evolution and they are familiar with it. Then when they get older, something new, new evolution appears but as the elderly, they struggle to learn new things, technologies and see it hardly to use those things for their life. We saw our parents like this and soon our kids will see us like this in future.