This is a thorny one that will piss off people no matter how you spin it. Some parents of small children are like dog owners and smokers, who can't imagine that they could annoy anybody with barking, defecating, shedding or passive smoke and discarded butts. I would attempt to say something like...the couple is looking forward to the joys of starting a family. Help them celebrate this event as one of their last adults-only gatherings before they change their lives forever. I don't think you'll avoid pissing people off but the White House has been getting away with this kind of stuff for four years. Good luck.