I often see high chairs sitting right next to the cars and it seems to work well.
There are a small number of "cars" that are actually tables/chairs placed with the car front and rear set like bookends. There are approximately 2 that seat 8 or more, or two parties of 4. I have only seen very large groups seated at these as they can squeeze in more for them here. There are approximately 4 that seat 6 and are very tight, I don't see more than 6 sitting here unless chairs are removed for the highchairs. The "picnic" tables at the back, used mostly for walk-ins, are all one piece tables, bench seats and umbrellas that don't move. The seats are attached, fit one person and there are usually 2 or 4 seats. Have seen a chair pulled up the the 2 seaters.
I would imagine you can request any of these seating situations for your group if willing to wait but if they have larger groups, the very large cars would be going to them first.
In the first picture you can see the large cars with tables (actually two tables split) bottom left and the smaller cars with tables towards the front and center. Second picture shows the smaller cars and in the back the saucer shaped umbrellas over the picnic tables.