Cracking the Easter Egg code

I've never had an Easter Egg before, but I know I am getting one on Sunday. I had this conversation with Äiti earlier.

Me: Where is the Easter Egg you bought me for Sunday?
Ä: What Easter Egg?
Me: The one you text Daddy about, you asked him to buy me one
Ä: um...no, I didn't
Me: Yes you did, here...
I then show Äiti the text message she sent to Daddy on her phone, it was in the 'sent' folder!
Me: See, you asked Daddy to get me an Easter Egg
Ä: How long have you known about this?
Me: Since Monday
Ä: and why has it taken you so long to ask me about it?
Me: I've been looking for where you hid it
Ä (now exasperated): and how do you know you'll get it on Sunday?
Me: I saw in Tescos that it said Sunday 12th April and that is on Sunday