Whether you are blending families or have a child or children with your fiance, weddings are full of opportunities to include children. (Of course, if you are getting married by a rabbi or cantor, you need to consult with them before making a plan).
If you are choosing a nontraditional ketubah text, including your children in the ketubah, the foundation of a Jewish family, can be a wonderful way for them to participate. I encourage couples to add some version of this line (location may be chosen by couple):
"Our [son/daughter/children], ________, join/s us as we celebrate our wedding and enter this new stage of our family life."
For blended families, it may be tricky to say 'our children,' especially at the beginning. In that case I recommend saying something like: "Our beloved [names]..."
Depending on their ages and your officiants' take on the ketubah, you may like to have your children sign your ketubah either as witnesses or as additional signatories. If there is room, some couples may like to add an additional section of signatures for the children with the above line.