I think being honest about the emotional side of it helps a lot. I try to validate the kids feelings that yes it sucks when daddy goes away for awhile and that its ok to be angry/sad/scared about it; sometimes I feel that way too. My boys dont outwardly talk about it much but tend to internalise and it comes out as bad behaviour. We also like to plan something fun for when daddy comes home so they have something to look forward to thats "normal" in our lives.

The under 5 age group is a hard one to deal with, its much easier with my older boys.