A 19-year-old man attacked the facility with a knife in the Polish village of Tomislawice, killing his 16-year-old ex-girlfriend. Media allege that unrequited love might be the motive for the crime.
Five people were hospitalized with knife wounds, with four others receiving on-site assistance.
The attacker was arrested by the police at his home an hour after committing the crime.
As many as 13 people were in the day care facility when the attack took place, according to the Polish news agency.