Interrupting is disrespectful.
I was 10 and I just had to tell my parent's friend, Mrs. Roush something. She held up her hand like a traffic cop, shook her head “no,” and kept talking to her friend until she finished, then I could talk. Now, all kids need to learn not to interrupt adults because it teaches a child respect. They shouldn’t interrupt parents either because whoever gets to interrupt gets to be in charge. So, in stepfamilies a biological parent can support a stepparent just by not allowing kids to interrupt.