I come from a similarly large family. I must admit that I've made comments like "What a large family!" or other references to numbers when I encounter them. I do so in awe and respect for the tenacity and patience the parent(s) must have, and I want to share that feeling. I could see how these comments might be construed as disapproving, even though my intentions are to familiarize and connect with the parents, rather than alienate. I'll certainly think twice before commenting in the future.