Our boy is a few months away from his 4th birthday... but he still puts darn near everything in his mouth. We are constantly talking to him about what should and should not go in his mouth, only food and your toothbrush... not toys, not sticks, not random junk you picked up off the floor, not napkins, etc. But it seems to just go in one ear and out the other. Even though he's told me he understands, and has sat there and told me "not in mouth" for various things, he still does it.
He's well past teething; they're all in. (Our dentist has even taken an x-ray to confirm that in the front since he's only got 3 front incisors.)
It does not appear to be hunger related. He routinely eats a good breakfast, lunch, afternoon snack and dinner. There doesn't seem to be a difference between days that he eats at day care and days that he eats with us; they report that he usually eats his whole meal, sometimes asking for more... pretty much the same thing we see. On several occasions when he's been seen chewing on toys, he has had the partial remains of a meal sitting on the table that he walked away from saying he was done.
When should we start to get worried? Any other suggestions for helping him stop this? (Aside from the choking concerns, the cleanliness/disease issues, and the various bad things that could happen to his GI tract if he swallowed something he shouldn't... there's some concern about what he's doing to his teeth... daycare just called and informed us he's had a piece of random blue pastic stuck between his front teeth for a while before they managed to get it out.)