It was a struggle to get my toddler into his pyjamas when he refused to cooperate.

cooperate 由前缀 co-（表示"共同"）和 operate（操作、运作）组成，字面意思是"共同运作"，引申为"配合、合作"的意思。这里指孩子不愿意配合穿睡衣的行为。