Parents are being warned to limit children's exposure to the sun as a heatwave is set to push temperatures above 30C (86F) across parts of the UK.
A heat-health alert has been issued for the majority of the country with the mercury set to remain "consistently high" throughout next week.
One computer model has shown temperatures could potentially even hit 40C (104F) in mid-July - although forecasters have expressed caution at this.
Parents and carers are being urged not to allow children to stay in the sun for long periods - and to "make sure they're covered in a high factor sun cream".
The UK Health Security Agency (UKHSA) and the Met Office have put in place a level 3 alert for the East of England, South East and London with highs of 32C (89F) currently forecast. A level 2 alert has been issued for the South West, East Midlands, West Midlands, North West and Yorkshire and the Humber regions.
A level 2 alert is issued when there is a "high chance" of the forecasted conditions, while level 3 means there is a "90% probability". The alerts will be in place from 9am on Monday until 9am on Friday.
Sheffield Children's hospital has appealed to people to "keep your children safe" during the incoming hot conditions.
"The first sign that a child is overheating is when they become grumpy or complain of a headache," the NHS Foundation Trust posted on Twitter.
"Get them into a shaded place that is as cool as possible. Remove any clothing you can, give them water to drink and get them to rest," it added.
The UKHSA recommended people should drink plenty of fluids and avoid excess alcohol during the coming week.
Physical exertion should be avoided during the hottest part of the day - and people should check on the vulnerable and the elderly who find the heat particularly challenging.
Dr Agostinho Sousa, head of extreme events and health protection at the UKHSA, said high temperatures are predicted for a "prolonged period".
He said: "Heat-health alerts have now been issued to the majority of the country, with temperatures set to remain consistently high throughout the duration of next week.
"Most of us can enjoy the hot weather when it arrives, but it is important to keep yourself hydrated and to find shade where possible when UV rays are strongest, between 11am and 3pm.
"If you have vulnerable family, friends and neighbours, make sure they are aware of how they can keep themselves protected from the warm weather."
'Potentially relatively long spell of warm weather'
Meteorologist Annie Shuttleworth said: "We're at the start of a potentially relatively long spell of warm weather for much of the UK away from the far North West, where it's likely to be a bit cooler and cloudier."
The hottest day of the year so far was during the last heatwave on 17 June, when a temperature of 32.7C (90F) was reached.
Ms Shuttleworth added that temperatures will "come close" to this year's high in London and the South East at the start of next week.
Parts of Scotland and Northern Ireland will also be seeing balmy weather, as across Aberdeenshire and Fife temperatures could be close to 27C or 28C, with 25C (77F) expected across Northern Ireland.
The hot summer days will also usher in hot and "sticky" nights. Ms Shuttleworth urged Britons to "keep the curtains closed during the day, especially if you've got a south-facing bedroom" and "keep ventilation going around your house".
The warm weather looks to be settling in for some time to come, according to Met Office forecasting. The average temperature for July is around 20C (68F).
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