I only worked part time when my children were very small, and returned to full time once they were at school.
IMO part time isn't easy, as you can feel out of the loop. Also, while you know which afternoon or days you don't work, it's silly to expect everyone else to know, particularly if there are several part timers. I work in a school with a two-week timetable, and some of our part timers have different non-working days in week 1 and week 2 - so it's daft to expect anyone other than the part timer to keep track of who works when!
If you are happy with working part time, then don't let it bother you - just do the hours you're contracted to do, and accept that you might feel a bit out of the loop simply because you're not there all the time