While the children are playing, you need to be attentive and ready to step in. You are there for the purpose of instruction, guidance and correction. If your child is too aggressive, you can stop the play and ask your guest, “Are you feeling afraid?” Then let your child know, “Your friend likes to play with you, but when you jump and flail your arms like that, it feels scary to your friend. Can you calm your body so your friend feels safer and can play better with you?” And then let them try again.