I remember when my kids were at primary school. They did definitely expect parents to accompany them on school trips (sometimes) when they were under 8 ... After that not so much.. Arthog was when they were 10. They definitely didn't take parents then.
I remember going on a school trip with mine when they were 6 and 7. I had two other kids dumped with me. They weren't even friends with my two daughters. And I didn't know their parents or anything. (Their parents weren't there obviously.) They brought no packed lunch with them and no money, and the teachers didn't even check if they'd got any food - or money!
So me and my 2 DD had to share our food with them. I also ended up spending about £20 on them as well. (£10 each.) On things they wanted/needed during the day. (8.15am to 5pm I had them with me and my 2 DDs.) This was about 20 years ago. I was not impressed. Having other peoples kids dumped on me, who I didn't even know. I'd got my own two to look after. I wish I had spoken up at the time and just refused, but I didn't so that's that. I think was blindsided and so that's why I didn't speak up... But I was really angry about it afterwards.
I think about 7-8 parents should have come along and only 5 turned up. Having to look after 2 children who were strangers ruined my day to be honest, and my 2 DD weren't impressed either. The children barely spoke to any of us. (Despite me trying to engage with them multiple times.) My DD said 'mom, why do they have to be with us?' I told them that their parents hadn't turned up, and the teachers (and the 4 other parents who had turned up) were already looking after 3-4 children each, and these children couldn't be alone.
I didn't even know these children and just had the teacher say, 'Mrs Sabre, Hannah and Lucy are with you and your 2 girls,; and then she fucked off and left me with them. I never went on another fucking school trip! Yeah I know it wasn't the fault of the 2 children, but I was still entitled to be pissed off.
Absolutely do not go @Cosmod . They have only asked you 3-4 working days in advance. Some schools behave like councils and housing associations with their social housing tenants. The staff assume most people don't work. and just send their workmen around randomly when they choose. There's no advance warning. Assuming you'll be in. The schools are often the same, assuming all - or most mothers don't work. (Or that they have such a trivial job that they can just favour the school's activities, and not turn in to work!) 