A three-year-old boy found wandering alone in Perth has been placed in foster care while welfare agencies investigate his family situation.

The child was found about midday on Friday, in the eastern suburb of Belmont, and was identified late on Saturday night after media coverage.

Authorities raised the alarm after more than 24 hours had passed and no one had called about the welfare of the child.

A spokesman for the Department of Child Protection says the boy remains in foster care while the family situation is assessed.