As far as I'm aware (and may well be wrong) it is not legal for a child to attend school until they are 5. Does anyone know where you stand if you're child has been attending but due to circumstance they stop attending, but the child is still not 5. The school would obviously be informed but due to it being half term no one is there to speak to at the moment.
They start school in the academic year Sept to August they turn 5. So if there 5th Birthday is 31st August they would only be 4yrs and a couple of days old when they started reception class at infant school.
Why are they not going back to school after the half term?
From age 5 to 17 education in the UK is compulsory, this is due to rise to age 18 in 2015. I am not aware of any legislation that requires you to commence education before the compulsory age of 5 as explained by cassa333, but some children commence education at age 3
If you are correct re the UK pidget, then it's changed since I went to school. I went before 5. I considered newly arrived 5 years olds to be late starters :-)