OK, so I don't haven't downloaded the phone app, so I'm not sure my comment is 100% accurate.
If you've expanded the sub boards, you want to make sure your setting is to NOT hide sub boards. If you hide sub boards, your post automatically goes to the main board. By keeping it visible, you just want to make sure you click on the link at the top that says WCF Babies before starting a message. Honestly, the only people who should probably hid sub boards are those people who don't even want to be reminded there's a baby board they don't want to look at.
All of this based on my two highly scientific "tests"