The incident was brought to authorities' attention after a 6-month-old baby died at Wake Med in May.
Authorities did not found any indications of foul play in that case and there were no charges filed.
But investigators said while investigating the baby's cause of death, they found a 2-year-old girl with ignored medical issues.
Officers also found a 5-year-old boy with physical injuries.
Smith bounded out of jail on $2,500 and Foster bonded out at $1,000.
The pair is set to appear in court on August 9.