First off congrats on the new addition to the family, i'm sure whatever tank you go with will provide him hours of entertainment cause all little ones love the pretty colors and decorations. That's awesome.
This maybe only my experience and hopefully someone else will agree while bigger isn't always better in most situations, I feel when it comes to aquariums it is. I don't mean go out and get a 125gal from the get go. But I picked up a 36 gal
bow front and I believe its a great tank to start with. Good amount of water where any water problem doesn't create a huge issue like a 10gal would. Give's you better options as far as stocking and decorations. But again it depends on your room availability and budget.
Either way let us know what you go with. Good Luck!!!