My sister is taking her two toddlers to SSL this year. I went with them last year, but we had problems. (Her kids like Sesame Street enough for her to overlook the mishaps from last year.)
First, when she ordered the tickets on the website it stated that childrens tickets for aged 3-6 (I think that was the age range) were half price of the adults. (That in and of itself is outrageous--how many adults do you know that's going to go to Sesame Street without a kid? and they have to pay $40?!) The site did not mention children under three, so we figured they must be free, just like at Disney.
WRONG! When we tried to get to our seats, the usher informed us that, even though the toddlers (we went with another couple) would be sitting in the parents' laps, they had to pay $5 for a "lap seat." We call that double dipping! So basically one parent had to pay $45 for their ticket.
As I mentioned, my sister is going again this year, but now she knows upfront what it will cost her. So just make sure you know all the hidden costs before you sign for your tickets--we missed the first couple minutes because we had to get the da** lap seats.