As a devoted grandmother who takes care of her two granddaughters once a week all summer, I would like to say first: aren’t we lucky? I know it is a blessing for me, and everyone seems to think it is for the girls, also. But I know exactly what you mean about not wanting to ruin your precious time together by having to discipline the older one all the time.
I think you have to abide by the disciplinary policies of your son and daughter-in-law; to do otherwise would be a violation of their trust in you. And it could also be confusing to your grandson. But time-out isn’t the only tool in your discipline tool box; use variations on the theme. For example, read a story to your granddaughter, holding her close to you, and say to him, “You have to listen from the doorway because . . .” and then mention whatever rule he had broken. Or, if you have the space to manage it, say something like, “You have to play in the room by yourself because I can’t trust you to leave your sister alone.” And don’t forget to praise him when he plays cooperatively with her and doesn’t annoy her.
Finally, let me offer the reminder that the very best discipline is prevention. Be alert for signs that trouble is brewing and then separate them as quickly as you can.
But mostly, enjoy!
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.