I personally would rather the parent ask me about this situation than just assume someone else was watching her child or that I had left her in the house unattended, so this question wouldn't offend me.

I try to put myself in the parent's shoes and would ask myself...is this parent asking this to be safe or is she too much of a worrier and not a parent I want to continue to deal with? I don't mind parents asking me things to clarify a situation. It actually worries me more when a parent doesn't seem at all concerned for their child's well being or questions the dcp at all. If a parent has been with me for quite some time and STILL doesn't trust me, than I would be worried and would consider terming.