Our sand ceremony did not include children but it included ALL of our parents. My mom has been married 3 times and my husbands parents are divorced. How we did it was:
mike mom aileen poured some of mikes (dark blue) sand into the vase, my mom and current step dad poured half of the sand(light blue) given to them into the vase after mikes mom and the other half into a vase that was going to make up my sand, my dad and step mom poured their white sand into the vase and into my sand and then my ex step dad poured his sand (glitter) into the vase and into my vase. We had the notary explain as they were pouring that the layers the parents were creating in the main vase represented the foundation they have layed in our lives. The sand that was poured into my vase by my parents and same with mike are what made us who we are. Then mike and I poured the sands together over our parents layers. After the ceremony our wedding planner poured the gel candle stuff we provided and made it into a candle as it hardened.
If you are interested I might still have the exact wording. Sorry for the run on scentences