Not at the age where I can contribute yet, but just wanted to say thanks to all those who contributed great thoughts and comments to this thread.
Daughter is only 1 and expecting another on the way but was already starting to think about these as well.
Was always planning on making both go through swimming until decently comfortable, we travel a lot and 80% of vacations have water and swimming involved. Wife is not a good swimmer and I don't want to be saving 3 people.
Karting and dirtbikes were always on my mind but never thought about the driving skills karting would bring over.
Will be following this thread closely for more suggestions.