Some caladiums are simply larger than others. It is very early in the season, yet, and so I think you should be patient. You did not mention when you planted them or how-such as in the garden or in pots. Caladium grown in pots for me are smaller by far than those planted in rich garden soil. But, generally, they are all "paper plate" size by the end of the season. Check my zone, Jusdewit, there could be some real differences, here. Check the GW forum for Aroids. There are experts there!

With caladiums, you should never let the soil dry out. Also, someitmes a bulb will send up flower spathes. These can be cut off to send more energy into leaf production. With a nice dark soil, heat, and plenty water, your caladiums should do well. Most varieties do well in shade, though some can tolerate sun. Generally, the thicker leaved ones tolerate some sun. If you have them out in full, broiling sun and don't water them often, the plants will struggle.