My son was 3 months old when I became pregnant again. I made matching shirts! Mine said Cupcake Baker and my belly said cupcake number 2. My sons onsie said cupcake #1 and my fiances said cupcake Maker. We walked into where my family was and just let them figure it out! Lol it took them a few minutes until they realized what it meant lol
I used my shoes my husband shoes and baby shoes with a coming soon sign and posted it on fb
For my announcement I had my son hold a sign up that said I'm going to be a big brother and the due date. We took a couple pictures and picked the best one and sent it to everyone. Since your first baby is so small maybe have the sign on a chalk board sitting next to baby then make greeting cards n send them out! Congratulations!
Bump for ya. I used my daughter to announce. I had her in a big sister shirt. They typically don't make them smaller than twelve months, but you could always do an iron on onto one of her onesies or jackets.