Make your Sim parents ignore their child for days, until he/she is hungry, tired and bored. The social worker will come and take him away. Make sure free will is turned off so there is no interaction between the child and the parents.

If your Sim parents completely ignore their baby in the same way, The Social Worker will come very quickly to take the baby away.
 Make your Sim child repeatedly miss school for days, and do not make him/her study or do his/her homework by using the bookcase at home (Sims can be home-schooled if they study every day from the bookcase). The teacher will come and send him/her to military school. The Sim won't be very happy, but it's a kinder way to go.
Removal by bad parenting.
Removal by bad grades.
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