The 33-year-old, named only as Jemma, was reported missing from her home in Merthyr Tydfil on Monday.
Her three sons and one daughter were also unaccounted for.
The children were named as Christopher, 11, Julian, nine, Maddison, seven, and three-year-old Stephen.
The five have been missing since Monday
South Wales Police
Urging people to "help us find them", detectives shared a photo of the family sitting together on a sofa.
The group were reported safe and well shortly before 1pm on Tuesday.
In a tweet, South Wales Police said: "We can confirm that Jemma and her four children, who were reported missing from Merthyr Tydfil yesterday, have been located safe and well."
South Wales Police had launched their missing persons appeal in the early hours of Tuesday morning.