 If you liked
Aishiteruze Baby★★
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 ...then you might like
Gakuen Babysitters
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Both MCs have to take care of children/a little child.
Both MCs share a sibling relationship with the child: one of them being blood-related to the child and the having a cousin type of relationship.
Both MCs care greatly fore their charge.
Both MCs have to take care of charge who have a tragic past: one of them having parents who died in a plane crash and the other having their father die and their mother leaving them to be cared for by distant relatives.
However, Ashiteruzu Baby is also romanced based which is unlike Gakuen Babysitters.