i_worker, congratulations first on actually managing to get an appointment to go to the Birmingham PEO, and secondly congratulations on all those ILR visas!
Of course you all now have visas with no conditions and so there is no reason to hold back on making claims to Child Benefit and Tax Credits.
Lots of applications for British Citizenship in a year's time?
A general comment about evidence to be taken along to a PEO .... take anything that might help your case. If the PEO don't actually ask to see that particular piece of evidence, well no harm is done, but the last thing you want to avoid is the PEO saying they cannot deal with the application on that day because they need to see some more evidence.
When my wife went to the Birmingham PEO in March 2002 for her ILR we took much more evidence than actually needed. In fact as it turned out the application was granted on the basis of the initial evidence which was produced, so we did not need to use any "reserve evidence".