Baby!siren!killer

Poor baby is hungry so he does what any hungry siren does - he sings.
Dumb baby doesn't know he supposed to do so on a cliff side so sailors are crushed on the rocks for him to eat. Fisherman lured in find him sitting in a tidepool, and take pity on him - he might be a monster but he's just a baby after all - feeding the hungry little guy some of the days catch.

Thus teaching this little siren that singing to humans gets him fish which is much easier and safer than trying to eat the humans