I went to Sesame Place when my son was three and had a baby with me as well. We went in August with my brother and sister and their families, as well as my parents. We were fortunate in that my sister in law knew an employee who got us tickets for $20/each. I think this park was well worth a $20 ticket, but not worth more than that. My 3 year old had a great time, lots of water play areas, but it was very crowded and hot. I thought to myself if I went back, I'd go at a cooler time of year, but for a mostly water-park, I don't know how much we could do if we didn't want to get wet.
With our group, I had 2 nephews ages, 11 and 12. They thought initially it was a really lame place to be going, but they did have a good time, just took them a little while to get past the idea they were going to Sesame Street, which they are way to cool for. LOL.
It's about a 4 hour drive for us, we also did that in one day. What a long day!!! We did not feel the need to close the park.
So, my advice is, go if you can find yourself a deal, or combine your trip there with something else fun to do, but don't spend $1000 to go there.
Good luck, and have fun at Disney.