A father whose four young sons could communicate only in grunts when authorities rescued them from a filthy Denver apartment faces up to seven years in prison when he is sentenced Tuesday.

Sixty-seven-year-old Wayne Sperling pleaded guilty to his second offense of child abuse in November. Authorities say Sperling, his wife and the boys lived in an apartment filled with cat feces and flies. The children, ages 2 to 6, were malnourished when they were found in October 2013.

Sperling's wife, Lorinda Bailey, was sentenced to 90 days in jail and five years of probation.

Prosecutors say it was one of their most horrific cases, but Colorado's child abuse laws kept them from pursuing harsher penalties because the children did not suffer serious physical injuries.

Prosecutors say the boys are improving in foster care.