How long will it take to heal a really childs knee injury? is glue good?

See below: If you are referring to a laceration (as referenced by the glue comment), then a knee laceration needs to be watched closely as it is a high tension area. If the glue closed the wound and the area does not open within 7-10 days, the likelihood of dehiscence (reopening) is low and the wound will improve over weeks. But, to be back to full strength, any wound/laceration care take year.