The incident was reported to haver occurred in the Halton Moor area of the city on Saturday evening.
A spokesman for West Yorkshire Police’s Wildlife Crime Unit said: “We are currently investigating an incident where a number of duckling may have been killed by a group of boys in an area known as the Beck on Halton Moor. “We believe this happened between 5-6pm yesterday (Saturday). If anyone witnessed the incident please call 101 and ask for PC 3.”
A surviving duckling has been taken into the care of The Wildlife Orphanage in Barlby, near Selby in North Yorkshire.
Annette Pyrah, who runs the wildlife rescue operation, said: “I received a call late on Saturday night to say a tiny duckling was arriving. A horrific story of cruelty unfolded and I was told that a number of 12-year-old boys had allegedly killed the mother duck and her ducklings with a stick.
“Another little boy, aged 10, was so upset at what he saw that he saved this little one which is now with us. Unfortunately she was so distressed she cried for two hours, so at 11pm I decided to put her in with another orphaned duckling which is slightly bigger.
“It’s always a risk putting a smaller baby with a bigger one, but I knew it was my only option to save her.”
She added: “I cannot for the life of me begin to understand why children should take a stick and bludgeon to death a mother duck and her ducklings.
“If those responsible for this vile and cruel act could have heard this baby duckling crying for her family then maybe they would think twice. I’m shocked and very angry. The matter has been reported to the police.”
Ms Pyrah advised that anyone who finds an orphaned duckling should not put it onto water as it will be quickly preyed upon by adult ducks.
“Orphaned wildlife need warmth, peace and quiet above all else, with a quick transfer to a wildlife rescue,” she said.