I would spend most of my time with the kids at the beach. That being said, I don't think that you should plan on seeing all of them while you were there - I would select a few of them to visit and spend some extra time at the ones that you do visit - the kids will not notice a difference between the beaches.
Additionally, I would skip many of the sites that you have planned with your rental car (i.e. condense your Wednesday, Thursday, Friday activities into 1 or 1 1/2 days - perhaps follow a full day itinerary of one of the tour companies and see some of the other sites on another day).
I should also point out that I have been to the Butterfly farm and it is true that they are more active in the morning. You may also want to go into the Radisson to see the exotic birds (great pictures) or go to see the iguana feeding at the Marriott (your kids would probably appreciate both activities and it would not cost you anything).
As for the TomCar tour, I doubt children are allowed in the car and if they are, I do not think that it would not be very safe for them. Stick with a rental car (a 4X4 with a hard top/air conditioning and rent car seats from your car rental agency instead of bringing your own) to see the island/go to Baby Beach.
You may also want to save the Jolly Pirates snorkel trip for when you are staying at the Westin (it is much closer). Also, while it is a great snorkel trip, there is not much cover on the boat to get away from the sun, hence, you should make sure that you bring the extra sunscreen for your kids (or perhaps take the shorter version of the cruise in the afternoon - it is a long time to have a young children on a boat).
A few other thoughts...do the Ostrich farm on a day that you are exploring the island (it would probably cut your day if you were to do it on the Saturday and you do not need to spend much time there), see if they will pick up your rental car at your hotel and the DePalm tour is not worth it, especially for very young children.