My son (age 12) dropped a 5lb weight on his toe. should we take him to see our family doctor? will he loose his toe nail?

Toenail injury: Ouch! - he may develop a subungual hematoma (blood collection under the nail). This is painful but usually doesn't cause loss of the nail. Trauma due to a crush injury can cause fractures of the toe bones. I would ice it and keep an eye on it. If he develops the hematoma - your doctor can drain it if it gets too painful.

Toe injury: Yes you should take him if the toe is swollen and painful to make sure he does not have a fracture. The doctor can tell you the probability of losing the toe nail.