My children are older but, I told my children straight away... I figured that because we're a family, we will go through this as a family. We went through the pregnancy, and loss of Noah together... we cried as a family and we grieved as a family... now with this pregnancy, we laugh as a family and they have been to the morphology scan with us.... if something does go wrong with this pregnancy, it is yet another thing we will go through as a family.
I agree that it is much better for your children to find out from you the exciting news... something that they can then go tell their friends