My (VERY HIPPY) uncle passed away when our DD was 3yo. Tho we don't live close to family, we had actually seen him within a couple weeks of his (unexpected) passing and my other uncle just suddenly passed away earlier this summer(DD's 5 now) so we have had to tackle this very subject.
I grew up in a house that wasn't religious (almost anti), and my husband went to church every Sunday until he was a (rebelious) teen, but he and I have always felt and describe ourselves as 'spiritual' if not affiliated with any specific defined/established religion.
Well before we were parents my husband and I witnessed a Balinese Hindu cremation ceremony and were really blown away by their take on death. Truly a more happy occassion since THIS life of suffering was over and the next turn on the karmic wheel was about to begin for the deceased. Death is really the ONLY certainty to life and attitude is everything. My name really is K. and that's our perspective on death.
So we talked about how now our Uncles are even closer because they are part of our hearts and with us always (not living a 1000 miles away). That they are part of the stars and watching over us, spirits free. They are done with their life of suffering and that we are really sad for ourselves because we miss them. But THEY wouldn't want us to be sad, we should think about them in happy ways or when we are doing something that they would enjoy to make sure to "bring them with" by making sure to think of them during the activity etc.
Since our DD did know these uncles (tho only actually met them a handful of times) some of the suggestions may not be applicable since mostly it was to explain why WE were so sad and crying WHEN they passed, but in your case the mourning is well over. Anyway, I hope that you may be able to take some of the non-religious or less religious twists.
kindly,
K.