I played clarinet myself from about age 10, DS in year 2 (nearly 7) brought letter home about lessons at school and wanted to learn so we agreed. I assumed he could just use my standard B flat clarinet, which is very decent and has always been looked after, but two lessons in he's brought home a note to day he needs a "little clarinet". Note also says we should be able to borrow from music service, but I've spoken to them and they don't do this and don't know what the teacher means anyway 
As it happens it's DS' birthday thus weekend so if we need to buy something I can roll it in with that, but I'm just not sure what I'm looking for - any ideas? I have found E flat clarinets online - would that be what we need?
Thanks all!
*disclaimer:have emailed teacher but no response yet.