We're doing the traditional unity candle for the mothers.
What about having six tapers surrounding the large unity pillar and each child and your parents (I am making an assumption they are present be in right or wrong, I don't know...

). When you go to light it, have each child, your parents, and the two of you light it at the same time. Again... I don't know if your wee ones can be trusted with open flames!
Are you using the unity candle from your original wedding? Can the two of you light that one in the traditional sense, and then turn around and light a second one that us just for you and the kids? It would symbolize the coming together of the two families and the coming together (and reuniting!) of your nuclear family.
There's always that sand option thing, too. I have personal feeling about it becuase I saw it so poorly done once; but for your situation, it might work nicely.
I will keep my eyes open. Your EM might have some thoughts, too... or the florist! Laura is excellent when it comes to those types of things. I will PM you her last name if you'd like (don't want to jus tpost someone's full name without their consent in a public forum like this!)
Hoe much longer is it until he's home?
xoxo