Kellyann Crosbie, 25, left her flat in the Knightswood area of Glasgow at around 1.45am on Wednesday.
She and her three children, a two-year-old boy and girls aged three and four, were last seen in Kirkton Avenue, Knightswood, in the early hours of May 1.
Police believe she may be with her sister in Knightswood or somewhere in the north of the city but want to check that the children are alright.
They are appealing for anyone who knows of their whereabouts to contact them.
Ms Crosbie is described as white, with long dark hair and a nose ring. All three children have dark coloured hair.
Inspector Jim McLaughlin, of Partick Police Office, said: “For whatever reason Kellyann left her flat with her children around 0145 am on Wednesday morning and not been in touch with family for almost three days now.
“We believe that she may be in the company of her sister somewhere in Knightswood or north of the city, possibly Maryhill. It’s possible they are staying with friends, however, even if that’s the case, we still need to know that the children are ok.
“While Kellyann has taken off with her children before without letting people know where she is, our priority is to make sure the children are safe and well and with that in mind, I would ask that she or her sister make contact with us so that we can all is ok.
“If anyone has seen Kellyann or the children in the last few days or who may know where they are staying, then please contact police as soon as possible.”
Anyone with any information is urged to contact Police via 101, quoting incident number 2403 of Thursday 2 May 2019.