No, . you don't have to start over.
You can remove the parents from each of the wrong children and attach the right children to them. If I put my aunt Vlasts's children under Uncle Frank, I would go to each of the four children--Edna, Mary, Patricia, and Robert and change parents. Uncle Frank's children would then have to be added to his and his wife Bette's profiles. So in the end, the right children are paired with the right parents. It's not too difficult. When the edit mother page comes up, it will ask you to replace the stated mother with another mother. Similarly, with the edit father page. Keep track of whiat you are doing. Sometimes I just go to the bottom of the page where it says remove "mother" or "father" and click the tab. I ten go to the right parent and add children.
I don't have a video on how to do it, but if you have questions as you proceed though the steps, I'm here to help.