I'm not sure about the word "embarrassed", but I had 3 kids in my wedding. Nephew (2), niece (3) and niece (4), and they were among my favorite parts of the day. The girls left the ceremony to go look for seashells and we have the cutest pictures of them walking with their buckets. Then my nephew stole my bouquet from where it was laying on the beach and then stood on my train and that's another of my fave pictures. I wasn't embarrassed at all by their behavior, or else i wouldn't have had them in the wedding. But that's just me, and I'm pretty low-key and didn't want an uptight ceremony, so what they did totally fit with my idea of a perfect wedding.
If you have a more "perfect" image of what you want your wedding to be, I think Julie's suggestion of having someone watch your son is your best option.