You are correct actually! I've just found out that we (he) is getting the full amount. I don't know very much about it but remember being told at the time he applied that he couldn't get the full amount bc I was subject to immigration control but clearly I was misinformed (doh)! Anyway, thanks for your help everyone!
Yeah, that's very strange... the amount he receives is based on the number of eligible children, not on your immigration status. The amount is £20.30 per week for the eldest child, and an extra £13.40 for each child after that.
The rules for child benefit did change recently though (Jan 2013), and now, if one parent in the family is earning more than £50,000 per year (presumably regardless of immigration status), then the household won't be able to claim the full amount of child benefit. It looks like if both partners are working, and one of them earns over £60,000, then the household will not be entitled to any child benefit. See here:
http://www.bbc.co.uk/news/business-17854937