Sing a Song of "It's My Turn"
It happens on every playdate -- two children want to play with the same toy. One way to help them to learn to take turns and work things out for themselves is to have them sing a song while playing with the toy. Once that song is over, it's the other child's turn. The song can be as simple and short as "Twinkle, Twinkle" for little ones or "If You're Happy and You Know It" for older ones.