If your child is regularly not finishing their meals, portion size is one of the first things I would check. It is a simple thing to adjust, and it changes mealtimes more than parents expect.

Most of us serve more than we think

A recent survey found that 80 percent of parents may actually overestimate how much their child needs.

That is not a criticism. Adult plates are the reference point most of us have, and small children need considerably less than instinct suggests.

Why a large portion causes problems

There are two separate issues, and they matter for different reasons.

It overrides self regulation

A larger portion size can override a child's self regulation. Over time, if you keep offering a larger portion than they need, they might just get used to it, and it becomes more than they actually require.

Children are generally quite good at regulating their intake over the course of a week or so. Consistently oversized portions work against that.

It can simply be off putting

For some children, a big plate of food is just off putting. It is the same for adults. Faced with a large amount of food, the response is not always enthusiasm.

So a child who leaves most of a large portion is not necessarily refusing the food. They may have been put off by the volume before they started.

Start small and add more

My advice is always to start small and add more.

You can always top the plate up if they finish easily and are clearly still hungry. Doing it the other way round means either pressure to finish, or food going in the bin, which just contributes to food waste.

Children are individual

There is an average, and portion guides work from it, but children growing on higher percentiles may need more food than a child growing on a lower centile.

All children grow at different rates, and their nutritional needs depend on age, gender, weight, height and overall activity levels. Appetite also varies day to day depending on tiredness, growth stage, whether they are coming down with something, and how the day has gone.

So treat guides as a starting point rather than a target to hit.

Stop encouraging a clean plate

We really need to move away from trying to force your child to eat everything on their plate, or encouraging it, because the aim is low pressure at mealtimes.

That means dropping:

• Asking children to eat up.
• Making pudding conditional on finishing their food.
• Rewards or praise for finishing everything.

Instead, listen to hunger and fullness cues. Be aware of when your child has had enough, and understand that you are not going to be encouraging them to finish everything on their plate.

Why this matters beyond one mealtime

One in five children are obese by the time they leave primary school. It is for reasons like this that keeping a check on portion sizes matters, alongside limiting foods and drinks that are high in sugar and fat.

Getting portions right is not about restriction. It is about not overriding a system that works reasonably well on its own.

Where to find portion guides

There are some genuinely useful portion guides available for home use.

• The Department for Education has a straightforward ready reckoner covering food groups.
• Some of the voluntary nursery food guidelines produced a few years ago have really nice photographs, which are visually helpful when you are trying to picture an amount.
• First Steps Nutrition Trust has some very good portion guides as well.

There is plenty of information out there if you just want to check what you are serving against something.

The practical summary

Start small. Add more if they want it. Do not comment on what is left. Watch for hunger and fullness cues rather than an empty plate.

If mealtimes are consistently difficult and portion size does not explain it, it is worth looking at how many different foods your child is eating across a week, and getting advice if that number is low.