Maybe an odd question but;

were there “no trespassing” signs or similar warnings posted at the construction site? Michigan law requires notice before the trespassing law applies.


One issue that may cause the delay you are seeing;

the operators of the construction site have to sign off on the charges. It may be as simple as it takes awhile for the notice of your actions to reach the person with the authority to say; yes, prosecute those kids. Charges may be delayed waiting for that.