Chaos ensues when a group of four teenage misfits sign up for a week-long school trip to a sleepy caravan park occupied by monotonous residents and the supernatural.

Hi Sam Garner.

1. Chaos sounds very unspecific here it makes the movie hard to visualise. So does the casual use of monotonous residents and the supernatural. Both don't make the concept clearer or more appealing, but only more vague. Try to focus in on where the major opposition/conflict will come from in the script. Is there some monster they have to defeat to return alive from their school trip? Are the residents really the problem? What sort of chaos are we talking about exactly?
2. The prime goal of your heroes is missing entirely, which makes this concept unfocused and like it could go anywhere, but nowhere specific.

I could see a field trip to a museum or to a famous landmark but a school trip to a sleepy caravan park seems odd.

With rare exceptions, it's better to cast a logline in terms of one protagonist, not multiple. Who is the (singular) protagonist, the alpha character, the "1st among equals"?

And what is his/her character flaw? What personal issue will the strange happenings force him/her to confront and overcome?

And what will they do once they discover the truth. Declare victory and go home? FADE OUT: Credit roll? IOW: it isn't a sufficient objective goal for them to "discover the truth" -- they've got to act on it, do something about the truth they have discovered. What is it they must do (objective goal)? What's at stake if they fail?

I have edited it so there is more of a plot: A group of four teenage misfits sign up for a week-long school trip to a sleepy caravan park occupied by monotonous holiday makers. It is not long before strange paranormal activity begins in the park and residents start disappearing. After a lavatory related haunting, the group decides to go on a ghost hunt for the truth.

What is describe is a situation, a setup for a plot -- but it is not a plot.

Ideally, a logline should answer 4 basic questions about the plot.

Who is the protagonist?
What's his objective goal?
Who opposes the protagonist?
What's at stake?