Most children have been spending their summer holidays racing around making the most of the good weather.

But there is a risk some could get dehydrated through sweating a lot in the heat or simply not getting enough fluid because they are too busy to think about eating and drinking.

A new study has shown a surprising lack of knowledge among parents in Brighton and with the prospect this year's summer heatwave becoming a regular occurrence, experts are warning parents to get to know what their children need.

The research shows that almost half, 48 per cent, of toddlers in the UK are potentially suffering from dehydration that may eventually lead to problems in both growth and development.

In Brighton, the situation is marginally worse than the UK average, with 49 per cent of toddlers not drinking enough.

The survey found that 80 per cent of the parents or guardians in Brighton questioned believed their toddler was drinking enough.

More than 2,000 parents with children under five were polled in the study.

ITV's This Morning medic Dr Chris Steele warns of the long-term effects of severe dehydration.

He says: "Ensuring your child is drinking enough liquid is vital. Without sufficient levels of liquid, young children may suffer from headaches, nausea, lack of concentration and, in the most extreme cases, liver or kidney problems."

On the strength of these findings, Dr Steele has identified a recommended daily allowance (RDA) to help guide parents, with key factors such as the active lifestyles of this young age group and the British weather taken into account.

The RDA level has been assessed as five 250ml beakers (approximately 2.5 pints) of liquid. This is in stark contrast to research findings which showed that 11 per cent of children in the UK are drinking just one 250ml beaker of liquid a day (approximately half a pint).

Dr Steele says: "I hope this RDA will act as a guideline to parents.

"Children of this age lead increasingly active lifestyles and it is important we realise this and cater to their needs.

"The difficulty parents face is that young children aren't always able to articulate their needs so it's difficult to tell when they need a drink. It can also be hard to get them to drink when they don't want to.

"The key is to ensure they have a range of options including milk, water and well-diluted juice."

There are a few useful signs of inadequate hydration parents should look out for. These include tiredness, inability to concentrate on simple tasks, irritability and loss of appetite.

In addition, parents should keep a check on their child's urine: Pale urine indicates the child is adequately hydrated.

Many parents think the most common sign of inadequate hydration is a dry mouth but this develops in the later stages of dehydration.

Encouraging children to drink can be a challenge so nutrition experts have drawn up a few tips to help: Drink with your child in order to set a good example.

Increase the variety of drinks you offer. Include milk, water and a child-friendly juice drink with no artificial sweeteners, added sugar, colourings or preservatives.

In hot weather, freeze their favourite juice in the form of ice lollies.

Soups and fresh fruit are also a good source of fluid.

It is not just toddlers who need plenty of fluid. Several schools in Brighton and Hove now provide free bottles of water to children in the afternoons.

The scheme was kicked off at St Andrews Primary School in Monmouth Street last year and schools including Hove Park secondary gradually followed suit.

Headteachers noticed that after a morning's studying followed by lunch, many pupils were feeling tired and lethargic in the afternoons with some children suffering from headaches and stomach aches.

Bringing in the water supplies has made a major difference, with both students and staff giving positive feedback.

The school water scheme was set up following research carried out by learning support service teacher Hilary Reed which showed the brain shrinks when it is dehydrated.