My father passed away unexpectedly last November. My little guy was only 26 months old when it happened. Even though they had spent a limited amount of time together, the time they did spend certainly made an impression because he definitely remembers his Grampa.
Tonight we were reading a story before bedtime and there was a Grampa in the book who looked like my dad...
2 year old: Mommy Grampa awake!
Me: Yes, honey that Grampa is awake.
2 year old: My Grampa sleeping forever.
Me: Yes he is baby. He loved you very much.
... big sigh