We told DD pretty soon after we found out, once it was confirmed by the blood test. Of course, she is a bit older so I wasn't quite so worried about how she'd handle it if I had miscarried - thankfully not a concern for us though.

We decided one afternoon to go shopping and called in at a baby shop to look at prams and cots. Took her a few minutes to wonder why we were there, then she guessed - she'd been asking for a little brother or sister for quite a while and finally has one!