I think my child may have broken forearm. What would that mean?

Forearm fracture. Most likely it would mean there is a break (fracture) in one of the two bones of the forearm, namely the ulna or radius. Depending on the location, type of fracture and amount of displacement or angulation will determine whether cast immobilization or surgery in necessary.
See a doctor. A fractured forearm means the bones in the forearm have broken. This needs to be seen by a doctor. An x-ray will be taken to evaluate the fracture to see if it is displaced. If it is displaced it may need to be manipulated to get better alignment of the bones and usually will require a cast for anywhere from 2 - 6 weeks depending on the age of the child. Occasionally fracures require surgery.