Birthday enquiries

This morning I asked Wilson about the date of his birthday. He in turn asked me what a birthday is and what happens on a birthday, so I explained about birthday cake and presents. He considered this for about half a second then told me it was his birthday 'tomorrow!' 

I thought this was a bit of a coincidence, and after I pointed out that there really wasn't time to organise any presents or cake by tomorrow he confessed that he had no idea when his birthday really was. I suggested he write to his mum, Mrs Vermilingua, to check the date.