My 20mo old was limping for a week on his right leg. He wasn't showing any pain either, he would literally run while limping and other than the limp showed no other signs of pain. Just like you mention, happy and unaware of his own limp. I kept thinking it would get better, but finally took him to my Ped and he had it xrayed at the end of the week.
Xrays according to the radiologist were slightly inconclusive but the Ped's office still reco'd a trip to the Pediatric Ortho. (And I probably would have gone to one regardless of what my Ped office said.) Went to Dr Ballock (CLE Clinic.) He took one look at the xray and said "fracture"! :) It is VERY common, in fact I think he called it a "toddler fracture". He pinpointed the spot on the xray and touched it on my son's leg, and THAT was the first (and only) time my son screamed in pain.
A full leg cast (just behind the toes up to just about mid-thigh) was recommended for 3 weeks (OMG, 3 WKS!!) but he was too wiggly and they only got half of it on and had to saw it off immediately. The Dr told me a bad cast is worse than no cast. He said the cast is not to help heal the bone straighter or better, only to keep my son from being in pain by stabilizing it. Well since he wasn't really showing any outward signs of pain other than the limping, I was just told to "do my best" to keep him less active (ha ha ha, like that's possible!) and within a few days (maybe 4?) after the Ortho vist, so maybe 2wks total, his limp was completely gone. He went in for a follow up xray a few wks after that and was completely healed, new bone growth was perfect, etc. The Dr said sometimes he's not even sure why they reco casts, as the little ones seem to do just fine without them.
Don't feel bad about letting him jump on the bouncy things, we don't even KNOW how mine got his! There wasn't a specific incident to trace it back to, so even had you kept him off, he could've been like my (very active) kid and just done it hopping around on normal ground! :)
Oh, and the good Otho Dr gave us a wink when we left from the follow up xray and said he'd see us again soon. LOL Some kids are just little daredevils! :)