IMO, 18 months is too young to figure it out on their own. It can be awkward, though, depending on the other parent and what they think is appropriate. In my circle at that age, we say, "Jack is playing with that ball right now (gently removing it from Jill if need be); let's find another one for you." And we do make an effort to entice Jill with something else. If Jack is really not upset, though, I'd let it go.
As they get more verbal, we encourage them to engage more directly. "Jack, tell Jill that you're using the ball, and when you're done you'll give it to her." We use this consistently in our playgroup, and it has worked really well. Amazingly, most of the kids "get" this, and really will go and hand their friend the ball when they're done.
-Erin
As they get more verbal, we encourage them to engage more directly. "Jack, tell Jill that you're using the ball, and when you're done you'll give it to her." We use this consistently in our playgroup, and it has worked really well. Amazingly, most of the kids "get" this, and really will go and hand their friend the ball when they're done.
-Erin