What happens to child support if a child is placed in temporary care and custody with a society?

Child support doesn't automatically stop just because a child is placed in temporary care and custody with a children's aid society - the underlying support order or agreement between the parents remains in effect unless a court changes it, since child support is the child's right, administered through a parent, and is treated as a separate issue from where the child is physically living day to day. That said, a placement with the society is exactly the kind of material change in circumstances that can justify asking the court to revisit support, since the paying parent's obligation and the recipient parent's need may both look different once the society, rather than either parent, is covering the child's day-to-day care.

In practice, whether support should continue, pause, or be redirected depends on the specifics - how long the placement is expected to last, whether either parent is still contributing to the child's costs, and what the temporary care and custody agreement itself says, if anything, about expenses. Don't assume you can simply stop paying, or that you're entitled to stop receiving, without addressing it through a court order or written agreement - unilaterally changing support without one can create arrears or other problems later. Raise the placement with a family lawyer promptly.