I haven’t tried it this way, so you should make sure the dairy replacements meet the needs of your child, but here is a suggested alternate ingredient list:
4 large russet potatoes
½ cup dairy-free heavy cream substitute (such as almond cream)
¼ cup dairy-free margarine or vegan butter
¼ cup dairy-free sour cream (many stores offer soy-based sour cream alternatives)
1 teaspoon salt
1 teaspoon black pepper
1 teaspoon dried parsley
1 cup dairy-free shredded cheddar cheese alternative (look for soy, almond, or rice-based cheeses)
4 strips dairy-free bacon substitute, cooked and chopped (an option is tempeh bacon)