I think that the verb ''may'' expresses permission. In the first sentence you are allowed to take the sweets, and the verb ''can'' expresses ability or possibilty, so it means that you have the ability or you are capable of taking the sweets, but they have a similar meaning.

Like others have said, may is giving you the option, can is the ability to do something. So for instance in America in early years of school, it is very common to be corrected from "can I go to the bathroom" to "may I go to the bathroom" because you have the ability to go there, you are instead asking permission from the teacher.

There really is little difference in most cases. They can be a bit different: "May" implies that you have authority over someone, so it is a bit loaded. If you caid it to your friend they might joke about you using the word, since you do not have authority over them. "Can" is just saying you are free to take some. So normally people would use"can" among friends, and "may' in a more formal situation.

"May" is more polite.