A toddler tantrum is usually indicative of one thing; somebody missed their nap. And this big brother is quick to point it out.
"Did you have a nap today?" he asks his sobbing sister, who shakes her head no. "You need one," he observes. (We loves this kid's judgment-free approach.) Baby sis seems to appreciate it too, gently patting his arm while responding, "No I don't!"
Does this sound like your house? If your toddler is resisting naps, do your best to keep him on track with a consistent schedule. But accept that some days, it's just not going to happen. This is especially true as sleep needs change and your child makes the switch from two daily naps to one. For the most part, toddlers need 12 hours of sleep each night, plus one to two hours during the day.