I cannot believe the guts of that woman. There is absolutely no fault with you telling the kids. I mean, not that I think it has smething to do with that, but you're married for peep's sake... This is not the 19th century when you were in "indisposed" when being pregnant and you had to stay home
. This is to be an amazing time for you. And also some of the kids will have siblings, they will know what it means to see a pregnant woman...5th grade, they must be 10 or 11. You're not luring them into a pit of horror. Pregnancy is an amazing thing. If you wanna be on the safe side, just give the kids a letter for their parents to let them know that you would like to speak to the kids about it and see what they say.