I have the Mirena, and I do not have children. It has been in about 6 weeks.
The insertion was not as painful as I expected. I took a stronger dose of ibuprofen (can't remember the exact dosage, it was a prescription) and some antibiotics one hour before the insertion. The doctor recommended I have someone drive me to the office, just in case I had a painful insertion.
It was smooth as silk. It literally took all of 15 minutes. They gave me an anesthetic, which only felt like a small pinch. She waited ten minutes for it to go numb, which felt pretty weird. Then, they measure your cervix, which is where I experienced the first bit of pain. It felt like an extremely strong cramp, but by the time it took my breath away, it was gone. Then the dr. clamped my cervix (which is where some women experience pain, but I felt nothing). Finally, the insertion. The insertion led to the same sharp cramp, but was over so fast I didn't even have time to tear up (and I tear up getting my eyebrows waxed!).
I hope this gives you an idea about what to expect, and when to expect pain. Every woman is so completely different, that it's hard to really know what will happen with insertion and after.
After the insertion, I was able to get up and walk within a few minutes (still a little numb). I was feeling absolutely no pain. I was scared that once the anesthetic and ibuprofen wore off I would be in pain, but there was none. I still have had very little cramping, which only occurred right before spotting. I started spotting about three weeks after the insertion, and I spotted for about two weeks.
My husband can't feel anything, although some women need to go back for a second visit to get the strings shortened. The "strings" are very thin, clear (like fishing line) that let you know the Mirena is still in place. I can only feel them when I insert my fingers inside myself in a certain position, and no other time.
Your doctor will tell you all this, but I am all about women being as informed as possible before going to the doctor! :) good luck with whatever you decide!