Here's another far-fetched idea...
If a child is placed fr adoption with a non-family member, Child Services remains in touch with the family for a period of time.
If a child is adopted by a family member, the background checks and maintenance are not nearly as thorough, particularly in an unofficial adoption (Ayla Reynolds stayed with her Dad while her Mom served a short jail term, and nobody verified that he was a suitable caregiver before she was placed with him). Often an aunt, uncle, or parent will take care of a child for a relative who is ill, incarcerated, or who dies, without filing official paperwork.
What happens if a child is adopted from overseas? Is the family monitored? What sort of background checks are run? I know there have been stories of pedophiles adopting small children from abroad because they are not usually in the care of a social worker.
Lately there have been a lot of stories about families adopting foreign children, only to get them to the U.S. and find they have serious issues, either as a result of their being mistreated prior to being placed for adoption, or as a result of spending an extended period in an institution. These parents often try to either sell the child or re-home the child (like it is a pet!). One family put a boy they had adopted on a plane back to his home country with a one-way ticket because he had adjustment issues they were not informed of prior to the adoption.
If a foreign adoption wasn't working out, could a parent lose patience and fatally injure the child for misbehaving? If this parent WANTED a child, and WANTED to love this child, but "snapped", the apparent loving care in choosing the polka dot leggings and pretty zebra blanket may imply regret over the death.