We live less than 20 minutes from this park, and decided to get season passes ("Passports") this year for DD13 and me.
It is not just for really little children, although they will be certain to enjoy it. There is a lot of Sesame Street theming, characters have frequent appearances for hugs and photos, and the parades are fun for little ones, too.
There is also a little pretend street with a store and a fire engine kids can play in/on. They will like the shows, and there are some water areas just for little children.
DD and I like the different water slides. There is one where a smaller child and an adult can ride together in a double raft, and there is actually a maximum height requirement for the child riding in the front of the raft; if you are over a certain height, they make you ride in a single raft.
The bigger water slides have a minimum height requirement. I think it is about 44 inches, which excludes toddlers and very little children; they have, in my experience, been very strict about enforcing the height restrictions. Of course, these rules are for the safety of the park's guests.
If you are in the area, I would recommend guests to take advantage of the "after 4" pass. It is only 23.99 if you arrive after 4 o'clock, vs 39.99 if you arrive earlier in the day. The crowds thin out about 5:30-6:00pm; of course, the lines are much shorter. The lines are also short during parades (just like in WDW!), so my older child and I take advantage of that.
BTW, if staying in the area, I would recommend a trip to New Hope or to Peddler's Village in Lahaska, PA, for some great shopping!!