A three-month-old baby is among the young victims of the stabbings at a house in Huddersfield.
A woman has been arrested on suspicion of attempted murder after three children were found injured at a house in Huddersfield.
Police were called to the property on Walpole Road at about 08:00 GMT and found a girl, two boys and a woman with serious injuries.
They were believed to have been caused by a bladed weapon, police said.
All four are being treated in hospital for their injuries, according to West Yorkshire Police.
Det Ch Insp Sam Freeman said: “Inquiries are ongoing today into what has clearly been a serious and distressing incident in Huddersfield.
“We fully appreciate the concern it will cause in the local community.
“Detectives are conducting inquiries to determine the exact circumstances of what has taken place and an arrest has now been made as part of those investigations.”
Officers remained at the property and “reassurance patrols” were taking place in the area, the force added.
Follow BBC Yorkshire on Facebook, Twitter and Instagram. Send your story ideas to [email protected].