As much as you might feel hurt, or that they somehow "hid" it from you...they are adults, and none of it is any of your business.
Please don't now go to them and bring the issue back up, because 1. you won't be welcome, 2. they must have had a hard time of it and 3. they don't need anybody to tell them it was wrong, especially after the fact.
Keep it to yourself, it's their lives.
It's up to the woman what she does with her body, but it takes two to make a baby in the normal way of things. It's sad for you, no doubt, but your sons are old enough to not let pregnancy happen in the first place - that's assuming that they didn't want it to happen, being as though they opted for such a drastic thing.
If you can talk to your son, I think it'll help you all.
Know what you mean Pudd. Its hard but we cant make them tell us. We would have offered to help if they'd told us but they told us after they did'nt want a baby. I went nuts and told her to go on the pill or my son to use a johnny. He was 30 at the time!