Children who eat the same meals as their parents are far more likely to have healthy diets than those who do not, according to research.

Eating the same food had a greater impact on a young child's health than any other factor, including social background and snacking between meals.

Dr Valeria Skafida, at the Centre for Population Health Sciences at Edinburgh University, also found that firstborn children had healthier diets than second or third born. In light of the study, which looked at 2,000 five-year-olds, the paper recommends that government advice to families should be kept simple to help establish good eating habits early.

Skafida said Britain was almost alone in Europe in "dumbing down" with children's meals in restaurants and at home, rather than encouraging them to eat what the adults were eating.

There is growing concern about the rise of ready meals marketed at young children, and about children being overfed with foods that often lack key nutrients.

"If children were eating what their parents eat – and, like the French, eating round the table – then we wouldn't have the iron deficiency problem we have," said Dr Colin Michie, chair of the Royal College of Paediatrics and Child Health's nutrition committee. He said children could have problems with deficiencies in iron, vitamin D and to a lesser extent zinc, and he was seeing lots of children with eating difficulties who were fed "sitting alone" by busy parents, and parents who made two or three different meals for adults and faddy children.

"If they sat together there are less chances of the kids manipulating the parent over food, as is quite common. Eating the same food as the adults is about behaviour, children copying the behaviour of the adults. There are particular issues in different parts of the population. For example, the Asian adult diet is a brilliant diet, yet many Asian mothers will fill their children full of milk, meaning they eat less because they are full of milk, which is great stuff but designed for baby cows and has absolutely no iron.

"Then we have the population covering themselves with UVB blockers very efficiently, and covering up their children. But so much that there's a serious vitamin D deficiency problem. Especially for black children, whose skins already struggle with the climate here.

"But we have a rising tide of obesity so we are trying hard to reduce energy intakes, and then we have a problem with the overfeeding of a lot of our babies. But where the deficiencies are in the micro nutrients, vitamin D and iron and zinc, these things are deficiencies which build up over time."

A lack of iron will hinder children's performance at school, for example.

Parents' busy lives were reflected in too many ready meals and takeaways in children's diets, said Judy More, a paediatric dietitian and member of the Infant & Toddler Forum, who is also concerned that a lot of under-fives drink too much milk: "It's critical up until 12 months, but then it's stopping children eating. Iron is a critical nutrient and children have a poor dietary intake of it." She said a big advantage of children eating with adults was that they were more likely to be exposed to a wider range of foods, key to keeping their diet balanced and healthy.

"The thing about ready meals is that a child will like one or two and that's what the parents will buy, so they are confining the children to a narrow range of foods. The whole thing about eating together is that children, especially under-fives, learn a lot by copying. They watch and see adults eating and learn to be less fussy."

The Infant & Toddler Forum has developed an initiative called Ten Steps for Healthy Toddlers.

Skafida said: "I don't want to stigmatise parents, they really have a hard time. Children the world over are picky and difficult at certain ages with food, and it becomes a catch-22 that you feed children what they will eat rather than struggle on. Unfortunately, the foods that are generally the most palatable are usually not too high in the lists of food that are the most nutritious."