Thanks ^^

Actually, it's a theory I've made.
1. An old man in Sinnoh not far away from the Daycare tells us nobody ever saw a Pokemon making eggs.
2. Arceus creates a Legendary Pokemon egg in the Sinjoh Ruins, meaning he can create an egg for ANY Pokemon.
3. There's this book in a library in Sinnoh telling us Pokemon and Humans were once considered the same species, and the original japanese version tells us they could even get married.

My theory is that Arceus creates eggs and send them to the Pokemon. Nobody ever saw a Pokemon making an egg because no Pokemon has ever made an egg. According to what the book says, it's possible that if an humanoid male Pokemon and a woman care enough for each other, Arceus might send them an Egg. And since the creature in the Egg is from the species of the "mother", then this egg would be an human egg. But it's just a theory.