There is a joke about toddlers that goes something like this: "If it's in my hand, it's mine. If it's in your hand and I want it, it's mine." That's a rather cynical and narrow-minded view of toddler mentally that I totally disagree with. A more accurate and positive view begins with the recognition that toddlers are curious and that they learn about the world through hands-on interaction. They don't really understand ownership. They are able to take turns if you step back and allow them to do so on their own.
Preverbal toddlers can only use toddler body language to ask permission. A preverbal child can't ask another child if she can have a turn with the toy in his hand. It is absurd that adults hold them to this standard. Instead of asking, a preverbal child will approach the other child, grasp the object, and attempt to take it into her own hands. If it comes away easily without tears or fussing on behalf of the initial holder, then permission has been granted by the holder, nonverbally. If the initial holder of the object grasps more firmly, cries, or wails, then he was clearly not done having a turn with it. The second child will either have to wait her turn or face the reality that her actions caused another child to cry.
Toddlers are very sensitive to the pains of others, and they can learn to be empathetic if we allow them the chance to practice it. Once an adult steps in, however, neither child is given the opportunity to learn about sharing. The initial holder doesn't get the chance to assert himself or to share. The other interested toddler doesn't get to learn how ask for a turn. She doesn't learn that her actions affect others, she only learns what happens to her (verbal scolding, time-out, or having the object taken away by an adult). Either way, adult interference seems to interfere with the very lesson we are trying to teach.
Putting this philosophy into practice actually works. I have been doing this with a friend of mine who shares my confidence in a child's ability to learn about sharing. Our preverbal toddler boys are close in age, and when they interact, we don't interfere. We are there to provide comfort to hurt egos or step in if either one of them is in danger. These little boys pass toys back and forth. They take toys away from each other, non-aggressively, and without incident. Occasionally, one of them gets upset or there is a moment of tug-o-war. But it passes quickly. Peaceful interactions resume as before. They resolve it. By themselves.