A bit of background first: My 6yo is generally very healthy, maybe a bit on the small side but bigger than his two healthy older brothers were at this age. He has mild pectus and Harrisons sulcus (both are weird shaping of the ribcage) which the paediatrician wasn't concerned about. No asthma or other issues.
We recently bought a trampoline for the garden which he was very excited about. DH built it last weekend and DS couldn't wait to have a go. He bounced a bit and then said that it hurt his chest and could only bounce a little bit, he's described the feeling in various ways such as "when I bounce it feels like someone is punching me in the chest" or "it feels like there's a rock in there bouncing inside me" He's tried the trampoline every day in the last week and each time has come off after a few minutes saying it still hurts. He seems otherwise healthy, happily rides his bike or scoots up and down the street so I think it's related to the movement rather than the exertion. He says it feels "a bit the same as when I run"
I will take him to the GP if it doesn't improve but wondered if anyone has had a similar experience.