Toddler is the perfect age to teach the child a lesson in generosity. That sharing is not bad and albeit good. You can begin by making the toddler focus on his belonging particullarly his favorite toy or maybe his pillow. That if he lends it to his older sibling, there is a sort of return. Parents sometimes let the toddler grow and wait until the child is age 7 before teaching generosity. There is a tendency for the child to be selfish that way.