不會遊泳可以snorkel but

you need life jacket (and most important of all, know how to wear it). About your 2 year old, the concern is if you are not a swimmer, it would be hard to safeguard a 2 year old in water. I've never been there in January, although I heard ocean water could be too cold to swim sometimes. The only place parking can be a problem is Waikiki beach. Parking is not much of a problem most of everywhere else. If you are staying at waikiki and do not plan to anywhere else, rental cars might cost you more to park at the hotel.

Here is what I would do (as I have done many other places)-during the days when you plan to spend time at a place such as waikiki, do not rent a car. When you are ready to move around, rent a car for those days. Should be easy to find a rental car company in Waikiki. Many hotels have rental car kiosks. Depending on the city, it is sometimes cheaper to rent a car in town than at the airport because some cities charge high airport fees, which you won't have to pay if you do not rent from airports.