My child repeatedly takes a toy that their sibling is using. How can I teach “Can I have a turn?” and waiting?

Stop the grabbing and describe the situation briefly: “You wanted it. It is Sam's turn right now.” Help return the toy, then make the changeover visible with a timer or a cue such as, “When this song ends.” Offer a similar toy or a small role while your child waits. During calm play, practise one way to ask—a word, gesture, sign, or picture—and notice the moment your child uses it in real life.