My Son Sometimes Takes Toys from Other Kids....

He doesn't understand. It's great that he has a way to ask for what he wants. It's okay for him to experience disappointment, and to cry. Parents usually want to prevent unhappiness in their children, but it isn't necessary---they learn about feelings, and about how life works.
I know a young child who was taught to say things like "Bye bye playground, see you next time!" to help him understand that he could leave a place where he was happy without thinking that it meant that he could never be happy again.
I'm thinking your son could think that way--bye bye toy, time for a different toy.
At his age, ownership has no meaning, sharing has no meaning, so no need to get too sophisticated with your explanations to him.

Sounds like you're doing just fine. He's still really little so don't expect too much from him. I agree with Catherine, below.

Kids aren't born knowing how to share, in fact it is the exact opposite! MINE! Is the key word. And if you understand the "animal" it makes sense if you think about survival, MINE means stronger, faster and being able to live. Fortunately we don't have to fight for survival, we have learned to share with each other and it is up to us parents to help our kids understand that concept. Ok. So knowing that, take a DEEP breath and keep re-enforcing "Baby, you need to share". He isn't going to like it, he is going to fight you and the other child. But if he does fight, take him out of the situation, take away the toy and give him something else to do. Um, and remember, he isn't even 2 yet! He isn't going to have the concept of sharing down for a long while so you are going to have to be patient!=)

I would just let him be if the other child seems ok with your son having the toy. At this age, they don't understand sharing or why it's important that they do so. When they get a little older (2-3 years) you can get into sharing more. But if he is playing with other kids his age, chances are they don't really care if he has their toy, and they may in turn take something from him (which he might be fine with if he's occupied with their toy). Kids this age are not really able to play WITH other children - they just play side by side with other children. They aren't really developmentally able to understand the idea of sharing yet, no matter how much we wish they would!