Every Day a Little Death - S1-E12
Corrected entry: Lynette's children are at home during the poker game, which we later learn takes place every week on Tuesday at lunch. So the three school-age children should be at school. Even if there's a good reason for one school to have a day off, the twins are at a different school from their brother, and the two schools coincidentally having the same random day off is so unlikely as to be Impossible, unless commented on in the script.
Correction: It is not Impossible for the two schools to have the same day off. It could either be early dismissal for parent-teacher conferences, or a teachers in service day, which coincide for the whole district because of the bussing system. It could even be spring break.