The 18-month-old boy was discovered with a bloody lip and wearing only a diaper at 9 a.m. Wednesday.
Police responded to 342 East 100th St. after receiving a call of child neglect. They said the parents were home in their third-floor apartment but unaware that the toddler was missing.
They were asleep when police arrived. It wasn't immediately clear how the boy got out and downstairs.
He was treated at a hospital and later released to the Administration of Children Services.
The parents were identified as 22-year-old Cruz Angel and 20-year-old Valerie Collins. Police charged them with reckless endangerment.
It wasn't immediately known if they had a lawyer.
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