Things You'll Need
Instructions
Take your Beldum and Ditto to a day care in any one of the towns in the game.
Leave your Pokemon at the day care.
Return to the day care after a little while -- there isn't a specified period of time; it's related to how many steps you take and it differs depending on the Pokemon's experience level. If you've waited long enough, they will have made eggs for you. If they haven't, keep playing the game for a little while longer before coming back to claim them.