My kids love love love this park. They ask to go to the train park all the time. Inexpensive rides on their railway and carousel make the place affordable, and you can picnic or buy food there. Their shops are reasonably priced with great chances to view their museum side as well. Never mind that the place is a huge park with a few play areas, one with swings and such, the other is like an old west town and the train goes by both.
Long story short... McCormick-Stillman is one of the best parks in the valley.