Start by tempering your milk chocolate.
Place a piece of baking paper on the kitchen counter.
Pour the chocolate into your egg shell molds and swirl it around well so that the whole mold is covered. Tap it on the counter a few times. This removes any air bubbles.
Turn it over and tap the back with something hard (e.g., a wooden spoon) so the chocolate drips off onto the baking paper.
Then use a palette knife (preferably thin) to scrape all the chocolate off the edges and onto the baking paper.
Now let the chocolate, both on the baking paper and in the shells, harden. Remember, the chocolate on the baking paper can easily be reused another time. It's perfectly fine.
Temper the white chocolate. White chocolate is somewhat harder to work with, especially because the working temperature of the chocolate is only 29 degrees Celsius (84 degrees Fahrenheit). This makes it a bit more solid and harder to spread. When you have an impatient 4-year-old helping, it can also affect the finish. But never mind that, she had fun, and the result was great, even if they could have looked a bit sharper.
Pour the white chocolate into the molds with the milk chocolate and swirl it around well. It can be a bit difficult, so you might want to use a brush to get it well distributed all around.
Let it harden.
When the shells have hardened, you must carefully tap the shells out of the molds. If the chocolate is tempered incorrectly, or you have some chocolate up the edge, you will not be able to get them out.
Heat a pan over medium heat or use a warm roasting pan from the oven to melt one inner side.
Now you can easily place it on top of another shell and use your fingers to make it look neat if necessary.
Remember, you can easily put a piece of toy inside before you assemble them.