What does it mean when it says caladiums can be overwintered indoors? Don't the bulbs need a resting period?
If they were planted outside, they likely did not survive the winter. They are only hardy to zone 10 and will die elsewhere in the winter outside.
If they were brought inside for the winter, you can plant or put them back outdoors when the weather stays consistently above 50F. They will start to sprout when they are placed somewhere that is above 50F and they get regular water.