DS1 is 3.5 years old.
Last month, DP and I took the DSs for a walk through the local woods, and rested for a while on a memorial bench. DS1 asked DP what the plaque on the bench said, and without thinking DP said that a man called Frank had died, and his family had bought the bench so they could sit on it and remember him.
Since then DS1 has been absolutely obsessed with Frank. How he died, where he died, why he died, where he's gone, how old he was when he died, whether he DS1 would die soon, when DS2 would die, will the cat die, will Grandma die before DS1 because she's old?
To make it worse one of the pets at his pre-school happens to be called Frank, and DS1 caused huge upset when he went in the Monday after the walk and annouced to everyone that Frank had died...
DS1 mentions Frank at least once per day, and often more, and it's showing no signs of letting up. He doesn't seem to be upset, exactly, but it's clearly on his mind. It doesn't help than Frank is just a name to DS1 (and us) so it's all very theoretical to him.
Can anyone recommend a good book or strategy to help DS1 understand?