I had mine done at a reproductive health clinic. We told the kids it was a "check up." Get a referral from the doctor, it would be easy for them. If you don't what the GP to know what you are asking, I would try looking them up online. My research indicates that the OTC kits you can buy have very degrees of accuracy. This is something were you want the most accurate test available.
They are young and it was easier than I guess a teenager would be.
Some will tell you not to do it, that what does it matter, etc.
I completely understand, you have to know. If it comes back you are the father, great. If not be prepared for a whole new dimension to this. (Happened to a close friend of mine) There are some guys here that can help you with that if it comes to it. IC would be even more important. Bio-dad is the easy part of the puzzle. Raising them teaching them, etc. Our environment is a much bigger factor in who we turn out to be than our DNA does.
Mine came back as mine. I know where everything stands now. Having any doubt was killing my relationship with my kids and my W. The unknown gave me an excuse to "give up."
It is a decision you have to make and live with. Don't let anyone talk you out of what you feel you need to do. There are many heated opinion on this topic and it can tend to be very sensitive on this forum. BTDT.
DS 6, DD 12
Dday 8/31/11. EA/PA. Lied to for 3 years.
Every truth comes to light in a long enough timeline.