I get calls from friends and family frequently asking exactly this question.
The 4 cm gash across the nose obviously needs to be repaired. Get off the computer and calmly take your child to the doctor or E.R.
What about the small cut? Which of those need to be repaired?
Clean or dirty?
If it is a dirty wound or the object causing the injury was dirty or rusty, a tetanus shot needs to be given if not up to date. Most children are up to date with school immunization requirements.
Location?
The location of the wound is an important factor. Contrary to public perception, the reason to close a laceration is not to prevent infection. If fact, the risk of wound infection is generally increased with closure. The main reason to close a laceration is for cosmetic benefit. (Can’t you just see insurance companies determining laceration repair to be an uncovered, cosmetic procedure). A small 1/4 inch laceration on the leg may not need repair whereas the same laceration on the face likely would.
Depth of laceration?
This is the difficult one to assess with a phone call. “How deep is it?”, often leads to a puzzled answer. In general if the wound is gaping open more than a couple of millimeters when the laceration is pulled open then it is through the dermis. Most lacerations 3 mm or more through the dermis benefit from repair. In contrary, A 1 inch laceration through the epidermis but not through the dermis will do well without repair. This is more of a “scrape”.
Clean or ragged?
Most ragged lacerations benefit from some debridement at the time of repair. The classic injury is a dog bit injury. Parenthetically, do not let your children near dogs that are play fighting or when they are eating.
Damage to underlying tissue?
This most commonly occurs in the hand. Even small stabbing lacerations in the hand can cause nerve or tendon injury. Numbness or lack of motion would be obvious indicators that evaluation would be necessary.