Police say they are not looking for anyone else after a 28-year-old man was arrested in Rotherham, South Yorkshire.
An early estimate suggests more than 2,700 people will have died from heat-related causes during the UK's exceptionally hot weather in recent months.
After a brief drop in temperature many areas will see heat and humidity build again this week
Cleveland Police says the children are confirmed to be safe after being checked over in hospital.
Residents near the Conwy fire have been evacuated, with at least 10 other fires across the UK this weekend.