Yes, he can eat off your plates. When my DD was under 3 lots of restaurants, particularly the signatures, brought out little plates of bannas or other fruit, cheese etc. for her while we had our appetizers.
I usually ordered milk for her and planned to pay OOP for it. I don't think one of the signature restaurants ever actually charged us for it. Maybe because we were also ordering wine, beer, mixed drinks...I'm not sure. We did pay for it at some of the other TS places. I think it just depended on the CM.
When she was 2 we ordered kids meals for her at some places and just paid OOP for them. It depended on what I was ordering. If it wasn't something she would like and enjoy sharing, I just paid cash for a kids meal.