One quarter of three-year-olds are now either overweight or obese, according to the Growing Up In Ireland report.
It's found that obesity levels rise from 5 per cent among children from the most socially-advantaged groups - to 9 percent among the most disadvantaged.
Children of less well-educated mothers are more likely to have energy dense food and less likely to eat fresh fruit or vegetables.
The report also points to parent styles which are 'low in warmth' or 'high in hostility' as being related to behavioural difficulties among Irish children.
The study has been running since 2006 and monitors the development of almost 20-thousand children.
