These days marriage is not only the legalization of the union between two people but the formal consolidation of a family : whether it is of children shared by the couple or of a merging of two former, independent families.
While the primary relationship to be celebrated at a wedding is that between the spouses, the importance of children can be acknowledged as a natural step in the ceremony.
So if the couple has been living as parents with their own kids the “marriage” is one for the whole family; if they have been living in a blended family, the ceremony is an opportunity to welcome the other’s children and acknowledge them, even thank them for accepting a new parent.
There are lots of ways to ritualize all different family circumstances to involve offspring no matter what age – older kids can witness, “give away” or do readings, young children can be spoken about in the ceremony ( even in the vows a commitment to them can be made), light candles, accept symbolic gifts… as with the rest of the ceremony, you are only limited by your imagination!
Here is one example which acknowledges step-children:
“____________ and _____________ would also like to acknowledge the support and role of their children. When two people come together and bring with them children of their own, there are concerns and challenges of each. Sharing a parent with another child, learning to live with a new person, learning the differences in attitudes and ways of life. It has been a growing time for each of the children and _________ and ___________ would like to say thank you to _______ and ___________ for the way they have accepted ________ and __________ as part of their lives.”