Since your goal is to hold thinking on long term results (18 years from now), you should think about storing your coins safely on your own hands. That is, to not rely on any third party online platforms to keep your coins stored. You need a hardware wallet and to control your own keys.
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I'm curious how the OP stored the Bitcoin they bought for the baby, they created a paper wallet? Bought a hardware wallet or any software Bitcoin wallet? It would be more amazing for OP to share how they manage to store the Bitcoin so just in case in the future, other will follow it too.
Just like me, I am planning to do it in the future for my children. Since I saw a lot of people having life insurance to their children while at very young age, so for me, I will do like what OP did.
i just wish that the OP was using Hard Wallet. Because the main problem in the long-term storage for years from a crypto asset is where it is stored. some of the cases that I have seen, many people hold their assets in several wallets, but some hackers are able to access the assets they have. I've even experienced this myself. Anyway, I don't expect him to use CEX to store his assets. I think that way because many lay people think that CEX is a safe and reliable place to hold assets long term.