I did this with my charges last year and didn't pay a penny. We queued up and kids were given 'passports' (which had money off vouchers for xscape) and we then entered through the shell of a plane complete with seats and controls that kids could play in. There was a smallish sandy area and they put on punch and judy shows.
They had a different set up every week.
Think they are hoping that you will go for the for the free activity and then have lunch/bowl/do cinema or something while you are there