I think the playgroup idea is even better than an open house, and would accomplish the same end. Parents of young children are always looking for cheap/free things to do. Offering a drop-in playgroup, advertised on social media, would get parents in the door, and if they don't need care, they might recommend the place to friends that do. Or stick up for your business when confronted with gossip ("what him? No way, we go there for playgroup and it's wonderful!"). When I was on mat leave I loved playgroups. If you're looking for older children, offer toddler/preschooler activities, but advertise as baby friendly, and hopefully the sibling sets with a parent on leave would go. You may have a niche cornered with Dads on leave too. Any military families in your area? I find military and teacher dads are most likely to take long leaves while the mom goes back early.