Oliver is born in the workhouse, and his mother dies soon after his birth. The state is unable to find his father. Therefore, Oliver, as an orphan, becomes the ward of the state. This leads to his being boarded at Mrs. Mann's home. She is paid a small amount of money by the state to keep the orphaned child, in what we would today call a foster home.
In Dickens' time, a foster home was not well regulated, as he points out, and officials like Mr. Bumble, the workhouse beadle, are just as glad if the children happen to die, as this takes the cost of supporting them off the hands of the taxpayer.
Oliver Twist somehow survives the cruel treatment he meets at Mrs. Mann's, which includes beatings, never a kind word, and a starvation diet. Dickens implies that he survives because of the companionship of other orphaned children boarding with him and because of his naturally optimistic spirit.
However, Oliver has now turned nine, which means he legally can't stay any longer with Mrs. Mann. Mr. Bumble therefore comes to pick him up and take him back to the workhouse where he was born. As Bumble explains to Mrs. Mann:
Oliver being now too old to remain here, the board have determined to have him back into the house. I have come out myself to take him there. So let me see him at once.
Mr. Bumble also tells her that the state has advertised and offered a reward to anyone who will step forward as Oliver's relative, but to no avail.