They are illegal to sell here. Its perfectly legal to bring them in.
No they are not, wouldn't want a child to be upset when the eggs get confiscated and don't want to see the "I was detained at customs because of my Kinderegg habit..

"
CBP Advises Kinder Chocolate Eggs Banned from Import into United States
(Wednesday, March 10, 2010)
contacts for this news release
Pembina, N.D. With the Easter season upon us, U.S. Customs and Border Protection officials in North Dakota want importers and the traveling public to know that Kinder Chocolate Eggs are banned from import into the United States. The prohibited Kinder Chocolate Eggs will be seized and destroyed upon entry into the country.
The eggs are prohibited because a toy surprise hidden inside poses a choking and aspiration hazard for children younger than three years of age. The Kinder eggs are hollow milk chocolate eggs about the size of a large hens egg, and are usually packaged in a colorful foil wrapper. The toy within the egg is contained in an oval-shaped plastic capsule that has small parts requiring assembly. Each egg contains a different toy.
The U.S. Consumer Product Safety Commission has determined that this product fails to meet small parts requirements for children less than three years of age. Additional information regarding unsafe toys and product recall announcements can be found at CPSCs Web site. ( U.S. Consumer Product Safety Commission ) CBP and CPSC work jointly to ensure the safety of imported goods by examining, sampling and testing products that may present substantial hazards.
Travelers are encouraged to visit the CBP Web site for useful information and publications such as Know Before You Go regarding what items travelers can legally bring into the United States. ( CBP HomePage )
U.S. Customs and Border Protection is the unified border agency within the Department of Homeland Security charged with the management, control and protection of our nation's borders at and between the official ports of entry. CBP is charged with keeping terrorists and terrorist weapons out of the country while enforcing hundreds of U.S. laws.