Hi there,
My DS is 22 months and we do the same thing from time to time. I was concerned that we were helping to create a really bad habit, but my mom said that once he is completely able to feed himself, that will be the new distraction and he won't need toys, etc. This has proven to be pretty accurate, because now we don't bring oodles of toys to his highchair. My mom also had a good suggestion though, for when DS needed a distraction. Have it be something educational, like a book, or a letter, or something that you can talk about while you feed him. Ask him about what colors he sees, tell him the animals, etc. We do that A LOT, and frankly I think it's made DS a really observant, good listener.
At this stage, I am wondering about the transition to a booster seat? He still sits happily in his high chair. Any thoughts?