Check for sharp edges. Before ever putting that costume on your child, check for things that may scrape or scratch. Sharp edges can most commonly be found on masks and other costume accessories. But also check the costume itself for sharp edges and other pieces that jut out.
Test for allergies to latex and other masks. The last thing you want on Halloween is to rush your child to the ER over a reaction. Do an allergy test at least 48 hours prior to your child wearing his Halloween costume. Check each mask label for the manufacturer's instructions on testing for allergies. General instructions will likely include exposing a small area of the skin to the material for a certain amount of time.
Test for makeup and accessory allergies. Face makeup and other Halloween costume accessories may also cause an allergic reaction. You might avoid face makeup and certain accessories, use hypoallergenic face makeup, or do a skin allergy test at least 48 hours in advance.
How well can your child see through masks and around hats? Tiny holes for the eyes are just one no-no when it comes to Halloween masks. Be sure your child can see fully when wearing any hats, masks, and face accessories. If your child cannot see side to side and directly in front of him without rotating his head, that's a bad sign.
Is the costume weather-appropriate? Sure, that fairy princess costume is adorable. But if it's snowing outside, your child better also have some cute warm clothing on top or underneath. On that same token, if your child is wearing a thick bear costume and it's 80 degrees outside, there better be some air filtration and/or fans inside of it.
Pay attention to length. Tripping over a costume might be funny. But it can also be quite painful. Be sure your child's costume is no longer than 6 inches above the ankles to prevent accidents on stairs and while walking or dancing.
Use appropriate accompanying footwear. Tired after a long day at work? You know that feeling your feet get? Help prevent that in your child on Halloween by making sure footwear is appropriate. Try finding shoes that are both comfortable and appropriate to the costume. Slippers and other dress-up shoes can be bought in a larger size to slip over more comfortable footwear.
Be sure costumes are bright, glowing, or have lighted accessories. Traffic can be busy on Halloween with all the activities going on. Make sure your kids are bright enough to be seen from a good distance.
Check faux weaponry for real dangers. True, these are supposed to be fake weapons. But that doesn't mean they aren't still dangerous. Look for sharp edges, removable parts, and other potential hazards to kids before sending them off to have fun on Halloween.