It is recommended children eat five portions of fruit and vegetables per day – about 400g.
The Journal of Epidemiology & Community Health study found those who always ate together achieved this – but those who only did sometimes came close.
Watching parents and siblings eat teaches good habits, experts said.
This study looked at just under 2,400 children at 52 primary schools in south London.
Parents and fieldworkers compiled food diaries at school and at home, ticking off all the foods and drinks a child had in one 24-hour period.
Parents were also asked questions about their attitudes to fruit and vegetables, such as “On average, how many nights a week does your family eat at a table?” and “Do you cut up fruit and vegetables for your child to eat?”
The study found 656 families said they always ate meals together at a table, 768 sometimes did, while 92 families never did so.
Children in the “always” group ate five portions of fruit and vegetables, compared with 4.6 in the “sometimes” group and 3.3 in the “never”.