J.
S.,
I think it is appropropriate to expect a three year old to sit at the table for a meal, unless of course you're talking about a five course meal or something! We have a three year old and a one year old, and we do expect the older one to show good table manners- staying seated on her bottom at the table, chewing with her mouth closed, using an inside voice, etc.
Here a few tricks that might be helpful:
Make a chart that shows on one side what is allowed at the restaurant and what is NOT allowed on the other side. Use simple sketches and maybe a few words. This is something you could do together, taking his suggestions as well as your own. Have him help you color it or put stickers on it. By doing it together, it helps him buy into the rules.
Play restaurant at home, using some stuffed animals. When the stuffed animals follow the rules, they get dessert! When they don't follow the rules, they have to go out to the car with Mommy and Daddy while the other stuffed animals finish their meal and get...dessert. How sad for the misbehaving stuffed animal! I bet your son will love this game!
During meal times at home, compliment your son when he shows good manners: "Wow, you're staying at the table without any reminders! I would love to take a big boy like you out to dinner!" And with the naughty behavior, "Hmm, that's sad. Only boys who sit on their botttoms get to go to restaurants with Mommy and Daddy." You get the idea- don't lecture, just give simple reminders.
And, I agree with the other two respondants; bring along a few things to do and slowly dole them out.
Finally, be prepared, both you and your husband, to take your son out to the car the very FIRST time he misbehaves in the restaurant. Do it without a lecture or anger, just say, "How sad. Boys who play under the table have to go to the car." Then you'll have to decide if he'll miss the whole meal, or if he gets another chance to show his big boy manners. I wouldn't give more than a few chances. I also wouldn't let him have dessert if he has to go out to the car more than twice. One of the keys to this kind of parenting is to not even break a sweat. In fact, I think I would take my plate with me and very happily eat my dinner just outside the car, with my little one safely strapped in his seat. He needs to see that he is missing out on something terrific when he misbehaves. Which also means he needs to have a good time when he is in the restaurant...make sure you include him in conversation and such.
It might not be the most enjoyable experience for you and your husband, but I betcha the next time your family goes out to dinner, it will go beautifully!
Good luck!!
J.