Terry,
depending on where you will be staying in Trinidad, you will experience travelling for hours in heavy traffic, as the
locations you mentioned may be pretty far away from your acommodation, and traffic in Trinidad is a mess.
Pitch Lake for instance is in La Brea, which is in South, Maracas Beach is on the north coast and Caroni in Central. Keeping your children in mind, i would rather not recommend to do more than what you have already on your list.
One spot comes to my mind for family excursions. Ask your tour guide for "La Vega Estate" in Grand Couva. It is a nature park with small fresh water lakes, Thelapia fishing, picknick sheds with BBQ facilities and a nursery with green houses etc. where you can see a lot of tropical plants. Many Trini families go there on a weekend but the place is open
everyday from 9am to 5pm. Check out
http://www.lavegaestate.com
Enjoy your stay in T&T !
Greetings,
Andy