Telling our other kiddos

Jillian • I was told I was infertile due to severe endometriosis. A few days before my scheduled hysterectomy... WE ARE PREGNANT!!
I need some opinions. Wednesday we will be 8 weeks. Together my husband and I have 3 boys. Him 2 and I have 1. When do you think we should clue in the kiddos to the new baby?? I am high risk and don't want to tear the kids up of something goes wrong. On the other hand I know they will be so incredibly excited as they have been wishing for another baby for 2 years! Ideas? Thanks!