I teach kindergarten and I waited for them to ask me! At around 15 weeks one boy patted my stomach knowingly and nodded his head and said "You have a baby in there." I said "Why do you think that?" "Because your belly is fat and if a woman has a fat belly it's a baby in there." His mom is 3 weeks ahead of me pregnant, and I had told her, so I figured she had told him, but she hadn't! funny things is though, he dropped it forgot about it.
It wasn't until about 19-20 weeks when I was REALLY obviously showing that they started to put it together.
"Is there a baby in there?"
"Yep!"
"Oh. I saw Sponge Bob last night!" was a typical conversation for awhile.
They are very understanding now, I can't believe they let me sit on the birth ball and don't play with it (and I have a few kids who don't listen to any other rules, so this one surprises me!) and they are always asking if things I do are healthy for the baby. I was asked to tie a shoe today and I told the boy to ask my co-teacher and he said "oh yea, you can't bend down, there's a big baby in the way!" cracked me up.
My hardest student has been touch and go. She is pretty nice *talking* about the baby and explaining why I can't pick her floppy "boneless" body off the floor when she's tantruming, but she has told me "I want to kill the baby" and lunged after me hitting and kicking. I thinbk there's some jealousy involved, she is in foster care (with a great foster mom) and really craves attachment and I don't think she likes that I'm sharing mine. Ahhhh the joys of being a teacher.