I think the email conversation below - to my Mum - sums it all up.
Markus and I were looking at photos of everyone today on my mobile phone. I have my favourites there, lots of friends and family and we quite often talk about them. He amost always recognizes "Aunty Cake" (ie my sister Kate), but no one else reliably.
Today out of the blue, he points to Dad and says Grandpa: then I find a picture of you and he says "Granny"
Wow!! Thanks, that's wonderful........... it's so difficult to retain any sort of connection with the boys, so many thanks for your continual repetition with photos and general occasional chat!
My Mum and Dad with Markus, February 2012 in Brussels