Complaints were made against hospital staff who apparently failed to spot fractures, a health trust said today.
An investigation has been launched at Mayday Hospital in Croydon, south London.
A statement from the hospital trust said: "Whenever there are a number of similar incidents the trust routinely launches an investigation to check if there are any underlying issues. This process is under way.
"In the cases where the family has made a formal complaint we either have already, or will be, meeting with them to discuss their concerns and answer their questions."
According to the London Evening Standard, Carly Moody, who is nearly two, was left with a fractured ankle for two days.
She had an X-ray at Mayday but staff did not see the break and the toddler was sent home.
Her mother Melanie Moody took her back two days later. She said: "She was crying and lethargic and couldn't put her leg down. My mother came with me. She looked over the doctor's shoulder and said she could see the clear break in the X-ray."
The newspaper said that Regan Mercer, three, broke both his arms but doctors only spotted one.
Zoe Swesi, one, had a broken arm, but she was not given an X-ray and her mother Jasmin was told to give her Calpol.