Dietitians and nutritionists say there are no "correct" timings for children to eat, although they should have three main meals a day and two to three healthy snacks in between. This means they should be eating about every three hours.

Their advice comes as more schools move towards a single-session model, which is raising concern among parents. Many say their children are eating at odd hours and having lunch at home around 3pm now that lessons end about 1.30pm to 1.45pm, instead of 12.30 to 1pm previously.

This is partly due to later start times at some schools. More schools have responded by introducing 10-minute snack breaks at noon so that children will not go home on empty stomachs.

The Ministry of Education said that schools decide on their daily schedules with student well-being as a key consideration.

Besides recess and a snack break, schools also ensure that students who stay back for afternoon activities have lunch breaks - which last 30 to 45 minutes - reasonably spaced from recess, said a spokesman.

Ai Tong School has even extended recess time from 30 minutes to 40 minutes so pupils have more time to eat, rest and play.

But some parents feel this is not enough. Ms Lim Wan Keng, 41, said her Primary 5 son usually does not eat a full meal at recess because he is still full from breakfast at about 6am.

He eats snacks like biscuits during the short break at noon and has a proper lunch from 2.30pm to 3pm when he gets home. "During dinner, around 6pm, he will tell me he's still full from lunch, and ends up eating less," said Ms Lim, a bank executive.

Similarly, weekday mealtimes can be a challenge for Madam Eng Chor Yong's children. Her 10-year-old son is usually still hungry after school, even after snacking at noon.

"Sometimes he eats light meals like bread and a cup of Milo during recess because the canteen queues are too long," said the 44-year-old online business owner.

Some schools like New Town Primary have reversed the timings - pupils have a 15-minute snack at around 9am and a 30-minute recess at lunchtime. Ms Goh Tze Tze, whose Primary 4 son attends the school, said she is happy with this arrangement as he can have a more substantial meal during lunchtime.

But other parents feel the current mealtimes - with the extra snack break at noon - is sufficient.

Madam Tracy Bee, who has a son in Primary 6, said: "We just have to work around the school schedule and train our kids to adapt."

Dietitians told The Straits Times that there are no established guidelines for "healthiest" meal timings.

Ms Jaclyn Reutens, from Aptima Nutrition & Sports Consultants, said: "What's more important is the frequency of meals and how much they eat at these times. Ideally, a healthy growing child should be eating three main meals and two to three nutritious snacks a day."

Ms Bibi Chia, principal dietitian at Raffles Diabetes and Endocrine Centre, said eating healthy is possible even during school. "It will involve bringing a healthier snack to school or selecting a healthier option at the school canteen."

Nutritionist Pooja Vig, from The Nutrition Clinic, said: "A good approach would be to look at what a child is eating over the entire day rather than worry about the timing of each meal."

Ms Michele Wong, principal dietitian at NutriWerkz, said parents need to adjust their children's meal timings: "The new lunch hour is around 10am, and that is feasible considering most kids have breakfast before 6am.

"Parents can also give them a more substantial healthy snack during the short break - like fruit or wholemeal biscuits - which is solid enough to keep them full so they don't have sudden hunger pangs when they reach home."

Ms Reutens said: "As long as your child is growing well, peeing and pooing regularly, your child is healthy."

•Additional reporting by Felicia Choo