I do field trips as well (we went apple picking this morning!), and when my families signed on and I told them that I frequently travel with the kids (library, play groups, parks, children's museum, indoor playplaces, etc), they were very excited about it. I have never ever interviewed a family who wasn't ok with me taking the kids out of the house for our adventures :) That being said, if it was something you talked up to them at the beginning when they signed on, then yes, it's going to be something they expect as that's why they chose YOU over someone else. I agree with a pp when they said that if you plan on reducing/cutting field trips you are going to need to make a formal letter addressing it and why so they will drop it!