We know what he thinks about education, the economy and Europe, but what about the really important stuff? Like how many nappies, exactly, has he changed in the last two weeks? And does young Arthur favour a three-in-one travel system, or a rugged off-roader? You can find out the answers to these and other pressing questions (and tell him what you think of all that tummy-patting) next Monday lunchtime when David Cameron visits Mumsnet to give his first interview since the birth of his third child. David will be online from 12.45pm. You can post advance questions for him here.