if you child was 5 this september then they should be at reception at a primary school. if they were 5 before the 1st Sept then they'd be in yr 1. not to worry though I started formal education whenI was 5 and a half as we lived in Germany for many years then came to the UK where I started yr 1 in the November.
Your 3 yr old doesn't have to be in education but would benefit from nursery - some local authorities do free placements for over 2's - 2 hours per day which helps with basic skills and socialising.
When you move to the UK or if you know the area you will move to it would be worth talking to the local authority to make plans and get a better understanding.
