Regular childcare costs are a necessary expense and must be included. Pension and life cover are discretionary and need not be included. AIB should have a mortgage calculator on their website. Why not enter your information on the template to see how much you can borrow?
I read somewhere that the main banks look for the following to be available after payment of your mortgage (which is stress tested at rates 2% above current rates) and all other non-discretionary expenses:
€1,250 for a single person
€2,000 for a couple
€250 for each child
So a couple with a child need €2,250 and the extra €50 is likely to do with the stress testing of the mortgage.