When my DH goes away it takes a couple of days for the boys to realise, then they get sad and ask when is he coming home. Mason and Angus are older than your boys so I can talk about what Daddy does ie he has a big long drive in the car to make special sausages in a different shop etc. I get them to draw pictures of what they will do together when he comes home.
We look at photos or home movies too.

Caleb is beginning to look forward to DH coming home this last week and seems to know when it's home time so I'm worried he will begin to miss him now.

Mine is going away for 10 days next week so we can be lonley together