I do not think getting a hardware wallet for a young baby will be right when only the seed phrase is enough to have access to the coins, I do not have to repeat what has been posted, follow BlackHatcoiner's post is the best. Just run Electrum on an airgapped device and generate a seed phrase, its keys and addresses, and send bitcoin to one of the addresses. All needed to access the coin is just the seed phrase.
True! But just to add for OP: if you already has a hardware wallet(lik everyone should), you can just:
1. reset your hardware wallet(make sure you have your backup!)
2. generate a new wallet for your kid, write the recovery seed down, and grab a wallet address
3. reset the hardware wallet again, then restore your main wallet
That way, you ensure security even if it's the case that you're not confident enough to create an airgapped device; because I think probably only a minority are capable and should create an airgapped device.