Kinder eggs are not legal for sale here in the US. However, quite a bit of Kinder eggs DID found their ways into the US through mail. The shipper will not get into any trouble because Kinder eggs are perfectly legal to purchase, sell, and ship in their country. The problem is on the US side. Normally, the receiver will not be troubled for receiving Kinder Eggs unless the person is showing signs that he/she got intention other than personal use. In another word, they will let you go for infrequent, small packages. The US customs do have the right to confiscate packages containing Kinder Eggs though.
There is a LEGAL way to ship Kinder Eggs into the US - Open the package and remove the chocolate. Once the chocolate and the toy was separated, it is no longer considered a Kinder Egg. It is okay to ship and receive chocolate and toys inside the same package. It was not as fun, but it did made things perfectly legal. :)
There are also LEGAL substitutes. Choco eggs and Zaini eggs are legal in the US and they are basically Kinder Eggs with a different name. You could legally have as many of those as you want. Even 99 Cent stores carry something awfully similar to Kinder Eggs from time to time.
PS: If one tried to sneak Kinder eggs past the customs IN PERSON, there could be a ridiculous fine up to $2,500 PER egg if one got caught. If those Kinder eggs passed the customs and one was found on you, then you might face a $300 fine per egg (if someone was really bored enough to charge you for possession).
Chocolate is the LEAST important part of a Kinder Egg. The main attraction is what's inside the egg because you'll never know what kind of toy you'll find in it. Putting a toy inside the egg shaped shell is fine if the egg was intended for someone else. If one puts the toy inside the egg her or himself, it ruins the surprise and defeats the whole purpose.
Got a daughter who LOVE Kinder Eggs. LOL