。
I gave my mother carnations for Mother's Day.
Literal
Mother's day [on-に] mother [to-に] carnations [obj-を] gave.
The double に does different work: the first marks the time of the event (Mother's Day), the second the recipient of the gift (お母さん). Japanese is comfortable stacking に for different functions in one clause. Carnations specifically — 赤いカーネーション — are the traditional Mother's Day flower in Japan, reflecting the US import of the holiday in the early 1900s.