Tess, my sons are grown (ages 30 and 40) but they hurt just as much as young children. The difference is they understand where as your children are too young to really understand. I have 3 grandsons (ages 15, 9, and 2) who miss their POP and do not fully understand. My 2 year old grandson for the last 2 weeks keeps asking me "where is POP?". I tell him he is in heaven with Jesus.
I have been thinking about Neal's birthday (June 12th) and Fathers Day, about what to do. I am going to talk with my sons about getting balloons, writing on them and going to the cemetary and letting them go. Maybe your children could do that. You don't even have to go to the cemetary to let balloons go.
Hugs to you and your children as I know this will be hard for all of us.