C.S.
Hi J.!
I SO remember those days! And 3 is such a hard age! (My opinion has always been that the terrible twos last 2 years...) Do you think that Andrew would respond to this?
This will require some extra time on your part for a couple days. Get a cup or small jar and put a piece of masking tape on it with "Andrew's Rewards" written on it. Then, get a jar of something that's his favorite that's small. (I used M&Ms, but you can also use raisins, etc. When they're older, coins and hew Lego pieces do the trick!) Sit him down and tell him that each day, everytime he shares, he gets an (M&M) in his jar. That means when Joseph has something you don't want, you get an (M&M) if you don't take it away. Then, you get to eat them before bed." Then, go into the room they are playing in and take the jar with you while you read a book or fold laundry, etc. Pretend you're not watching, and when Andrew takes a toy, cut in and say, "Oh Andrew! Don't you want an M&M? Why don't you give that toy back to Andrew and I'll put one in your jar?" It only takes about 2-3 times reminding Andrew to share that he'll get the hang of it and then he'll really make sure you KNOW when he's sharing. Then, right before bed (or after supper), give him his jar and say, "Wow! Look at all the M&Ms you earned. I wish I could eat all of those. You get to eat those now because you shared so well. When you're finished, we'll start the sharing game again right away." The second jar is still one that you have to monitor, but for the next several days, there should be at least a little improvement in behavior. If you can't go to where they are playing (like fixing dinner), bring them to you in the kitchen with toys and monitor them there.
The thought is that Andrew should see sharing not as a deprivation but rather something he gets something better from. I was concerned when I started this that they'd get hooked on candy and go back to old ways once the week was up. But, it seemed to have a lasting effect and I would pull it out again if things started getting bad again.