Ragemage
Wept for Zion
Why is cereal watching him? Do you have a source?
I'm not playing through the game again to take pictures of it but essentially Father says he did it to give you hope that he was still a 10 year old boy, and thus make your revenge against Kellogg all the more potent.
You can also tell it's set during modern times rather than 10 years after Shaun's kidnapping because in the memory, Diamond City Radio is playing, and Travis is still the announcer. Travis is only 20 or so, he definitely wouldn't have been around 40 years prior to work as a radio DJ. He wouldn't have even been a sperm yet.
That's pretty much the only explanation given. Shaun wanted to give you hope, I guess, that he was still a child, and thus make you hunt for him more fervently and kill Kellogg instead of giving up.