OH that poor baby! I hope his little legs heal alright! My Schnauzer/Poodle when he was very tiny yet took an unexpected leap off of the grooming table ... he suffered a pretty bad concussion. Scared me to death .... made my table a safer place after that.
I have a 5 lb poodle that is 11 weeks out from his second broken leg ( thankfully, they were not at the same time). He had to have plates put in because his breaks were just above the wrist, so his legs were splinted rather than casted. The biggest problem has been the exercise restriction he's still under; as he heals he feels better, so he wants to run and play with the others. I let him walk in the house, on a leash, but carry him up and down the stairs to minimize the stress on his legs.
My vet put him on vitamin supplements that contain calcium, in the hopes it might strenghten his fragile bones; I've also gotten suggestions through this forum on exercises that will help his muscle tone, and again protect his bones.
The best advice I got from my vets was to be patient, that young dogs heal well when given time.