These boys are diving into what is called a bog - which is a wetland that accumulates a deposit of mosses called peat or sphagnum moss. It usually occurs when the ground is mostly acidic. It's very important for the biodiversity despite its dodgy-looking appearance.

 

In all probability, the boys would've made it to the side because of the open lake or water source beside it.

 

It looks disturbing because it looks like the ground just pulled them in.