We went to BBWWS in February with a 2 year old and a 6 year old. We only paid for one child, on arrival the younger one was given a hat which was unexpected. When we were seated we had expected him to be on our laps but found it no problem for us all to shuffle up a bit to accommodate 4 of us across 3 seats. The seats are not bench style but individual ones that are quite flat and very little gap between them, so I sat across 2 seats and the youngest had 1/2 of a seat to himself.
Our waiter checked our tickets and told us he'd give the youngest some food as well but would put it on one of the adults plates, when he dished up he mentioned whose food was who's. He also got given drinks as well.
We took a few snacks for him just in case, but I have read of some people getting given food and some not, so I guess it maybe just down to luck. The food was really nice and plentiful so even if you're not lucky, you could likely share 3 meals between 4 with such young kids.
We only paid for the cheaper tickets and the staggering of the seats is massive so never any problems for little uns to see the action. You'll love the show and great value for money with plenty of drink refills as well.