We shouldn't have to tell you this, but if you see signs telling you to stay off the museum exhibits, then stay off them: an 800 year-old coffin on display at Prittlewell Priory Museum in Southend in the UK has been damaged after being knocked off its stand by a clambering child.

According to CCTV footage, the kid was lifted over a protective barrier by his or her parents assumedly in an attempt to get a photo of them in the coffin. After the coffin was damaged, the family made off without reporting the incident.

That left staff with the job of discovering and fixing the coffin, which has since been completely enclosed to prevent future damage – which of course means other visitors can't get as close to the artefact.

"The care of our collections is of paramount importance to us and this isolated incident has been upsetting for the museums service, whose staff strive to protect Southend's heritage within our historic sites," Claire Reed, the conservator responsible for repairing the relic, told Mattha Busby at The Guardian.

"My priority is to carefully carry out the treatment needed to restore this significant artefact so it can continue to be part of the fascinating story of Prittlewell Priory."

The priory was founded in the 13th century by Cluniac monks – monks keen on restoring the traditions of early monastic life, including caring for the poor. As many as 100 monks would've lived there at one point, historians say.

It's a unique bit of history, and the sandstone casket that was damaged is the last of its kind – which makes it all the more baffling why anyone would let their kids sit inside it, presumably for a photo op.

"It's a very important artefact and historically unique to us as we don't have much archaeology from the priory," says Reed.

The coffin was discovered in 1921 with a skeleton inside, possibly the remains of a senior monk. The artefact has been on show since the 1920s, but "nothing like this has ever happened before" Reed told the BBC.

Unfortunately this isn't the only example of people acting dumb inside art galleries and museums. Last year a clumsy attempt at selfie-taking left a 126-year-old Portuguese statue shattered beyond repair.

In the Prittlewell Priory Museum, the damage is thankfully not as bad – the coffin can probably be fixed by experts for less than £100 (about US$130).

That doesn't excuse going over protective barriers and interfering with ancient artefacts when you know you shouldn't. 

"You can put all the risk assessments in place but you really don't expect people to try to get into the artefacts," said Reed.

You can read more about the incident and see more pictures of the damage at the Southend Echo.