The correct answer is Social loafing.

Social loafing is the tendency for individuals to expend less effort when working collectively than when working individually. In this case, the child is putting in less effort because they believe that their individual contribution will not make a significant difference to the outcome of the task. This is a common phenomenon in group settings, and it can lead to decreased productivity and efficiency.

The other options are not correct:

• Group polarization is the phenomenon where groups become more extreme in their opinions after discussion.
• Compliance is the act of following the rules or instructions of another person.
• Conformity is the act of changing one's behavior or beliefs in order to fit in with a group.