Former teacher here. Why are you getting worked up about this at the start of the school year? These residential trips happen in the summer term, so no one will be asked to commit until then. If certain classes/year groups are going, then those tutors/teachers might be encouraged to go, but the school only ever wants to send as many staff as fulfil the staff/student ratio. They don’t want to have to pay for more supply staff than necessary to cover absent staff!
All teachers have a life outside school by the way, you’re not unique just because you have a child. Teachers are not paid extra for school trips, in the same way they are not paid overtime for other things - but a good school might offer a day off in lieu the week you return (or they might not).
If you’re new to the profession, and expecting to be paid every time you do something over and above your timetables lessons, you are going to be very disappointed! Planning, marking, assessing, making resources, attending Parents’ Evenings are all things you’ll have to do.
Remember - teachers get paid over the full 12 months of the year, including generous holidays, which is meant to account for the ‘extra’ stuff you might do in term-time.
Are you one of those teachers who expects to leave on the bell every day and always complains about doing anything extra-curricular? Because that won’t get you very far if you’re looking to advance through the ranks.
Residential school trips are tiring but also very rewarding in my experience and I went on a few. But again, they usually ask for people to volunteer initially so no one is forced to go.
You sound like you haven’t been a teacher for long if you don’t understand how this works. But in that case, ask more experienced colleagues in your school if you’re unsure about stuff - don’t ask Mumsnet because most people here haven’t a clue about Teachers’ Pay & Conditions, which are quite unique to the profession.