Babies that display two key aspects of appetite grow unusually rapidly up to the age of 15 months, research has shown.
This potentially increases their chances of becoming obese children, according to experts.
A second study found that 10-year-olds with a lower satiety response (SR) - making them less likely to stop eating when they feel full - were genetically more susceptible to obesity.
Satiety responsiveness (SR) was one of the measurements taken to monitor appetite in infants.
Scientists studied data from non-identical same sex twins born in the UK in 2007 who had different levels of SR and food responsiveness (FR), the urge to eat when seeing or smelling tempting food. Within pairs, the baby that was more FR or less SR than its twin grew faster.
At 15 months old, both traits separately caused a twin to be about two pounds heavier than its sibling.
Lead scientist Professor Jane Wardle, from the Health Behaviour Research Centre at University College London, said: "Obesity is a major issue in child health.
"Identifying factors that promote or protect against weight gain could help identify targets for obesity intervention and prevention in future.
"It might make life easy to have a baby with a hearty appetite, but parents may need to be alert for tendencies to be somewhat over-responsive to food cues in the environment, or somewhat unresponsive to fullness."
The findings appear in the journal JAMA Pediatrics alongside a study by another UCL team.