Baloney. You don’t segregate English speakers from the trip, the most likely of all to help these kids learn English.
Yes, you do actually some of the time - if you're actually interested in truly educating children as opposed to just indoctrinating them in socialist ideas like "all children are equal and there are no differences in ability" as all too many schools are nowadays.
Grouping by ability is by far the most effective way of educating children quickly and efficiently - taking children at the same level and putting them together and targeting their specific needs, rather than trying to do this in a group of widely disparate needs. When it comes to language teaching, that means taking the children who don't speak a language well and putting them together for specifically targeted lessons.
And when you look at the primers used in early primary school to teach children how to read, one of the best ways to help young children from ESL backgrounds to learn English quickly is to expose them to the common nouns and verbs in those books in real life environments. Visiting zoos and farms is a good way to do this as so many of these books use animals as basic concepts for illustrations - you need the child knowing that the animal they are looking at is a tiger is you want them to start working out that the initial sound in that word is a 'T'.
I'm a history teacher at one of Australia's most successful independent schools - a role I came to fairly late in life after a military career because of the influence of my wife weho is one of the senior English/Primary Literacy teachers at the same school. She's been running programs that work to create highly educated and literate children for about thirty years at this point. We know what works.
Yes, you want the children to have considerable contact with native English speakers - but not all the time. You need targeted work to meet their needs, and at the same time, it means the kids who already speak English can get lessons aimed at their higher level rather than having to put up with lesson always being aimed at the kids in the class who need special help, and finding themselves being used as tools to teach others who are at a lower level, rather than being given their own opportunities to learn.