At what age would you feel comfortable letting your LO go on a daycare field trip?

My LOs go to the same daycare and the older class goes on field trips almost every week (sometimes just in and around the city and sometimes further away on chartered transportation) and the younger class usually stays at school. Most of the time, school is open for the younger ones when the older ones are gone, but occasionally for all-day field trips school is completely closed. There is an upcoming all-day field trip and school will be closed for the younger LOs, unless they go on the trip, and they are always welcome on the trips. DD is only 18 months, so she will just stay home that day (luckily, my job is flexible). I'm not sure at what age I will start letting her go on all day field trips. With my older LO, we didn't have to deal with this because his old daycare didn't offer field trips when he was young, and he started the new daycare with field trips at 3.5yo. At what age would you let your LO start participating in field trips?