I'll be depositing funds in their accounts regularly, which will keep sitting there for about 6-10 years, so I'll be looking to accumulate some sort of interest during that period. What options should I consider for this?
Earning interest from crypto is a bad idea. Because it means dealing with centralized platforms or DEFI, both of which have high chance of being scams or simply failing because they are not sustainable. Also "crypto" itself is not a good long-term investment that can last 18 years. Because the lifecycle of an average altcoin is just 2-3 years. And even high profile "good projects" like Ethereum lack the fundamentals that could inspire confidence in their long-term survival.
So buy Bitcoin and hold it yourself, and when you child is ready, teach them how to use it and transfer the coins to them.