With both parents we just gave the very happy phone call.
With my DD, i found out about the pg 3 weeks before her 12th birthday, she had wanted a baby sister or brother for a long time time so we thought it would be cute and a very happy surprise if we told her on her b/day. In the morning DP woke her up to into the room to collect all her presents, we told her after she'd opened them all that there would be another after school.
I had brought a beautiful birthday card which on the front said "to a special sister" i just put in a arrow and wrote "BIG" between special and sister. Inside i wrote a little poem about her finally getting the birthday wish she'd always wanted and about being a big sister etc. (it rymed) She was so wrapped!! She still has the card.