Could just be the time of year, the younger ones are looking for new perching/nesting spots and being up in the attic, you're more vulnerable to their stupid navigation problems.

Net curtain solution is a good one, closed windows are stifling at this time of year. Another thing you could try is hanging old CDs on strings in the window, they catch the light and breeze and are pretty good at deterring the things from crash landings which I expect is more your problem then them actually wanting to come in.