From the SPM technical documentation:

Another important part of work-related expenses is paying someone to care for children while
parents work. These expenses have become important for families with young children in which
both parents (or a single parent) work. To account for child care expenses while parents
worked, the CPS ASEC asks parents whether they paid for child care in the previous calendar
year and how much they spent on that care. The amounts paid for any type of child care while
parents are at work are summed over all children. The ITWG, following the recommendations of
the NAS report, suggested capping the amount subtracted from income, when combined with
other work-related expenses, so that these do not exceed total reported earnings of the lowest
earning reference person or spouse/ partner of the reference person in the family. This capping
procedure is applied before determining poverty status.

See #4984 for work-related expenses.