A mother struggles to cradle her overweight 18-month old daughter who already weighs more than 3.3 STONE - double what's recommended for her age and height.Chubby Dan Dan has been taken to a specialist clinic because her mum and dad can’t work out why she’s getting so fat - stopping her from walking.Dad Cheng Lichao and his wife Feng Xiaochun, from China, took their tubby tot to hospital looking for help.They say they’ve visited a string of hospitals but doctors have been unable to explain their girl’s obesity.Mum Feng said Dan Dan was a normal weight when she was born. She added: "She started to grow quickly from one month old.When she was one-year-old her weight had reached 15kg.“She has a big appetite. Each meal she must eat nearly a big bowl of rice and drink a lot of water."The couple also have a 5-year-old daughter, who weighs just 2st 7ounces.