How much should my son pay toward replacing the headphones he broke?

The receipt said $120. My ten-year-old put his $14 savings on the table and asked whether that meant he couldn't buy anything until next summer.

He had borrowed his sister's headphones after she said yes, then left them on the sofa and sat on them. The headband snapped. She is fifteen, saved for them herself and wants the same model again. I immediately told him he would pay for a replacement. I hadn't checked the price.

He gets $3 a week. His sister says changing the amount now would mean she carries the loss because he's younger. My partner thinks fourteen dollars is enough to make the point and says the rest should come from us. I don't want to turn one careless afternoon into months of debt, but I also don't want my daughter to hear that lending her things means accepting the damage.

We haven't bought anything yet. Should his contribution reflect the full replacement cost, what he can realistically pay, or something we agree with both children? And who should explain the change to the promise I made?