Is having muscle strain something to worry about? My wife is upset since my son's doctor visit.

Most likely not. Children with muscles stain usually do okay by conservative treatment, in rear occasion they need surgery. Thanks.
Generally not. A strain is faily common if there is some kind of history of injury and one can expect full recovery especially in a younger patient. However if this is a chronic or recurring problem this just may be term that a nonspecialist physician is applying to a condition which they are not familiar with. In that case second opinion from a specialist (orthopedic surgeon) may be indicated.