Danny Parkes, 31, and his wife Victoria, 34, made the heartbreaking discovery when they attended little Henry’s burial plot at Pontefract Cemetery late last month.
The grave is shared by ten stillborn babies and is often decorated with colourful flowers, toys and memorabilia.
Mr Parkes, of Caslteford, said: “Our part of the grave is normally covered in lots of little ornaments and trinkets, all very personal.
“But pretty much everything was destroyed.
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“It’s not about the monetary value it’s about what they meant to us as a family.
“I was really annoyed when I saw it and my wife burst into tears. It’s absolutely devastating.”
The couple, who laid Henry to rest at the site after his birth in October 2014, said they found pot ornaments smashed, grass scattered over the grave and flowers ruined.
Mr Parkes said: “Only one corner of the plot had been affected by the damage.
“But the whole thing was covered in grass which makes us think it could have been caused by a lawnmower, maybe caught the edge as it was turning or something.
“I don’t think whatever has happened is intentional. But it is upsetting.
He added: “It’s the first time anything like this has happened.”
Mr Parkes said he and his family were left with no choice but to clear up the mess and replace the trinkets on Henry’s grave.
Glynn Humphries, service director for environment and Streetscene at Wakefield Council said: “We are very sorry to hear Mr and Mrs Parkes have been upset.
“We fully understand how distressing it is for families when memorials are spoilt which is why we always take extra special care when working around them. We have checked with the team who look after this cemetery and there haven’t been any accidents.”