My T is happily married with one kid...I am single and never plan on having children. It honestly does not impact our relationship at all.

Keep in mind, T's have to help clients deal with LOTS of things that are completely outside of the T's own personal experiences. So, having kids, being married, or not, shouldn't really impact the quality of care they can deliver. Now, if it makes you uncomfortable, then that's probably worth discussing with the T.

That said, my first two T's had kids that were my age, and that actually was a problem for me, because I felt too much like they were trying to "mother" and "control" me, and a lot of my issues revolve around my own mother and her constant need for control. My current T is only 10 years older than me and has a child that is about 10 or 11 years old, so I feel more on equal footing with her.