Can I include past daycare field trips under childcare expenses if I needed them to attend the field trip so I could attend school?

You can only claim expenses related to child care, and not education or transportation expenses. 

If you're not sure if the field trip fees are eligible, you will can contact the Canada Revenue Agency (CRA) and confirm it with them. 

If you are in Canada or the United States, you can call the CRA at 1-800-959-8281. If you are elsewhere, you can call 613-940-8495. This page has more ways to contact the CRA: Contact the Canada Revenue Agency