Is there a specefic proxedure. I can’t seem to find anything on the net. Kids who are in infants school, is there a formal way or taking them out or something?
Ask the school? Each has its own procedure.
Re: how do you inform the school you are moving abroad
Talking to school doesnt help? 
Re: how do you inform the school you are moving abroad
Please visit website of school and find out procedure of long absence.
Contact your school or speak with teacher, they can help you.
School administration may also helpful.
If this does not help, please let us know.
Re: how do you inform the school you are moving abroad
Formal way is to write an application and request long leave. 
Re: how do you inform the school you are moving abroad
send them a letter and that is more than official intimation that your child is moving. that should be sufficient and it should suffice the ego of the school boards.
Re: how do you inform the school you are moving abroad
You mean you are leaving the school to get admission in abroad school. In this case you have to consult authority (accounts/administration section officer or Principal) and apply for school leaving certificate or transfer certificate, migration certificate, character certificate, pay dues, apply for marksheets if any.
Re: how do you inform the school you are moving abroad
I would write a letter to the head with details of dates etc.
Are you going back to pakistan? Have you and the kids not settled here?