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.