unity sand

So I need opinions on this please.....

1) My fiancee has a daughter from a previous relationship, and I have been involved in her life since she was only a month old, so I am obviously close to her (well as close as you can be to a 11 month old). When we get married, she will be almost 3, so I want to do something special with her at the ceremony and was thinking of doing the unity sand ceremony. That would involve us both pouring sand into a large pillar vase..does this sound like something ok to do with a 3 year old? And would it be ok to do this and the unity candle with my fiancee?