I bought 3 cheap onesies for my 4 month old and used markers to decorate them. One says "Only Child Expiring October 2013", another says "Only Child" (which is crossed out) and then "Big Brother" underneath. The last says "(Almost) a big brother".
We have our 12 week u/s tomorrow and then I'm posting them on fb!
Re: Announcing on Facebook
Sounds cute!! With my second I had my first wear a Big Brother shirt holding the u/s pictures. We posted pictures of it on Facebook and let people figure it out.