Hiya, my children are in the school I teach in...it is a primary. We had a long think about it at the time, and decided it would be ok, but I think it depends a lot of the personality of the child(ren), your own personality (as in, can you detach yourself from them throughout the day) etc...
I also have a few colleagues at my school who are in the same situation, and we switch for math sets (ability level) where some actually are then teaching their own child...I personally do not agree with this, but my colleague who does it is excellent at it, and keeps her professionalism to a top most priority (there was concern at first at parents giving their own child extra priveleges etc..).
I leave the teaching of my children to my colleagues, who I trust, and if they have specific concerns, they come to me about it. We do not discuss my children unless there is a specific problem or reason to do so (as you would have with any parent), I go to open evening appointments, but at a different time, because obviously I am still doing my own at the same time as my colleague is...but it allows DH to be able to attend as well.
From the other perspective, I currently have four "staff children" in my class, and there too we have no problems...every so often we discuss their child in the staff room, but it is only with the Mum there (one is a teachers child, the other three are TA's children), but I have no difficulty with doing it...in fact I kind of enjoy it, as it means that your colleague has great faith in you as well you get to know the parents that much better and can hence know different ways to help their child (based on home-school relationships)