i did not know i had 2 catholic students

i did not know i had 2 catholic students until i asked their classroom teacher why they did not come with the rest of the students that meet with me on wednesday. she said they were excused that day due to attending mass. I find it interesting that catholics would send their kids to our school or they be accepted given our church's view on catholicism. Theres a catholic k through 8th and a catholic high school in the large city nearby.