A quick post about my experiences with arm injuries involving both my kids at age 3 years
First incident: after lifting boy up by his arms (bad idea, I cringe now when I see people do this to kids) the arm became limp and painful. Waking up next morning no change, A&E diagnosed a pulled elbow (no X ray). Fixed by a quick manipulation of the arm. No long term after effects.
Second incident: boy fell onto shoulder while play fighting big brother on the grass. Pain and couldn't move arm at all. Waking up next morning no change, X ray at A&E diagnosed proximal humerus fracture (upper arm bone close to the shoulder). Initially a little concerned operation might be needed as this is where tendons attach to the bone but this is apparently rare. They gave him a collar and cuff and said it would be a one week wait for the fracture clinic. That seemed a long wait given the pain he was in at the time, so we arranged to see a private orthopaedic consultant a couple of days later by which time he had greatly improved. The follow-up medic said that usually these fractures self-heal in about 3 weeks but that extreme caution is needed in the meantime to avoid further trauma to the break. Keeping him off nursery for the next week or so to avoid any accidents and will try and keep the collar and cuff on him but he's moving it well now and saying it feels better 3 days after injury.