Jo-Anne
Although I enjoy both islands, if I had to skip one, it would be St. Maarten. However, don't think you cannot enjoy the islands if you don't do excursions. We travelled with a just turning 5 DS and DS's 7 and 9. We went to the beach on each stop on the Eastern. St. Maarten is actually the easiest, just take the water taxi from the pier to the first stop. Get off and go to the beach right there, Great Bay Beach. It is very pretty and you can see the ships in the harbor the whole time while enjoying the beach. We rented some chairs and the kids played in the water for hours. When we were ready to go back, it was a very short trip back. It is also very reasonably priced.
Water taxi - $5pp for an arm braclet that lets you use the taxi all day long, and children under 12 were free.
Chair rental - rented two chairs and umbrella for $10.
Couple of suggestions
1. pack life vests for your kids. I know they take up some room, but they made me feel more comfortable with my kids playing in the sand right near the water.
2. Stop at a store near the port and buy some sand toys. My kids were entertained for hours.
You also might be interested in reading my trip report, which deals with travelling with kids of similar age, and the types of things we did in port etc. Here's the link.
http://www.disboards.com/showthread.php?s=&threadid=332407
Have fun no matter what you choose!!!
disneyeveryyear
You might want to give St. Maarten another try. I was there 13 years ago as well (Nov 1990), and they had had a very large hurricane come through 6 months to a year before (don't remember the name, but it was a well known hurricane!). Anyway, the streets had been washed out in the town by the port, and the pier I believe was damaged as well. Everything was very muddy, etc. While the town is not that great now, it is much better than it was then for sure. They have a very nice new pier, and the beach as stated above etc.[