Here's a selection of Swedish warning and no trespassing signs that could come in handy, adding some local colour.
"No trespassing. Guardians are responsible for their children."
"No access for unauthorised. Parents who let the children play in this workplace are responsible for both accidents as well as damage caused. The labour management."
“Access, photography, etc, prohibited. It’s prohibited for unauthorised persons to access, photograph or otherwise depict or describe this area or bring explosives within the same. Trespassing is penalized with fines or prison.”
"Lethal voltage. Unauthorised have no access."