First congratulations on over wintering such a dramatic tropical plant as your Elephant Ears or Colocasia plant. The aphid you see  are most likely hatching from eggs left from the summer outdoors but aphid are easy to control. Use a a mild dishwashing soap such as Ivory or use an insecticidal soap made for houseplants . Just make sudsy warm water and spray this onto the plant stems and leaves as well as the soil. Rinse and wipe the plant down after half an hour. Repeat every few weeks if you see more aphid appear. Once the weather warms up your plant can go back outdoors and the soap and water spray can be used again if you see a build up of aphid. A spray may not kill the eggs protected in sacs in the soil or hiding in leaf petioles  but soap will break down the waxy covering on the aphid body so contact with soap is a simple way to control soft bodied insects.  Keep growing, Marianne Binetti