Start/End Dates	2011-04-27 through 2011-05-31
Country	United States

Details

Participating Toys"R"Us locations distributed an event egg that will hatch into 1 of 3 Pokémon. This same event was available over Nintendo Wi-Fi Connection in Japan at the beginning of 2011. Players of Pokémon Black and White can receive the egg at Toys"R"Us from April 27th, 2011 to May 31st, 2011. Below is the full press release.

Press Release

Get a Secret Egg, pick up special Pokémon TCG packs, and discover new Pokémon at a special Toys“R”Us event beginning April 27th!

Coming up in the Pokémon: Black & White animated TV series, Ash is given a great responsibility—he must care for a delicate Pokémon Egg until it hatches. Watch episodes every Saturday through May 21st on Cartoon Network to find out which Pokémon will hatch!

You can follow in Ash's footsteps with your own Pokémon Egg! Visit participating Toys"R"Us stores from April 27th to May 31st to receive a Secret Egg distribution for your Pokémon Black Version or Pokémon White Version game. Carry the Secret Egg with you in your game until it hatches to find out which one of three secret Pokémon you'll get!

While at Toys"R"Us, look for a special Pokémon Trading Card Game offer: you can purchase Pokémon TCG: Black & White booster two-packs that include a secret promo card featuring one of the three Pokémon that may hatch from your Secret Egg!

Head to Toys"R"Us starting April 27th with your Nintendo DS™ system and a copy of your game for the Secret Egg distribution, and check out all the other amazing Pokémon products, including special packs of Pokémon TCG cards!

Source: http://www.pokemon.com/us/news/vg_bw_secretegg-2011-04-11/