When toddlers and babies roll their eyes it's usually because the toddler or baby is drowsy and sleepy and ready to take a nap or go to sleep for the night.
My toddler would always roll his eyes when he was tired and although he insisted he was not tired he would go sit on the couch and would fall asleep.
So in the case of my toddler boy he would always roll his eyes when he was tired.
He also rolled his eyes back in his head when he was an infant and it's a normal thing that some babies and toddlers do.
At first it looked freaky to me when I saw my infant son at the time roll his eyes back as he was falling asleep but I asked his doctor about it and he said it was very normal and nothing to worry about.
A toddler may also roll their eyes when they disagree with you about something or you want them to do something and they get mad at you then they roll their eyes.
Or the toddler may think what you're doing is crazy etc and they roll their eyes.
But a toddler or baby rolling their eyes is most commonly a sign of drowsiness.
Toddlers will also sometimes throw tantrums when they are tired and need a nap.
My son used to always throw a tantrum about 10 to 20 minutes before his nap time.