Purim is the festival most obviously designed for children, and the one most likely to overwhelm the smallest of them.
A grogger is thrilling at four and genuinely distressing at eighteen months. Decide in advance where the sensitive child will be, and give them a job away from the loudest point rather than expecting them to endure it.
A child who wants to be a digger rather than a character from the story should be a digger. The costume is about participating, and a child arguing about their costume is not participating.
Packing and delivering food to other people is concrete, repeatable, and the child can do most of it. Let them decorate the bags, choose who gets which, and hand them over themselves.
Very young children usually cannot sit through it, and many communities run a short children's version. Ask what yours does — practice varies a great deal.
Decide the rule before the day, out loud, and say it once. Negotiating it in the moment on Purim is not a winnable position.
Part of our guide to The Jewish year with children.