Did you know the Easter Bunny, portrayed nowadays as a rabbit, was originally a hare? In pre-Christian times the hare was the traditional spring animal because it was associated with Eostre (Ostara) the goddess of the dawn, spring and fertility.
It's easy to see the connection as Hares are very fertile animals. They can have up to four litters in a year, and each litter can have up to four young (leverets). The females can actually conceive a second litter while still pregnant with the first.
Quite why they bring chocolate eggs is still a bit of a mystery. There's a lot of theories, what with Eostre being the goddess of fertility, and the egg being a symbol of fertility, and the hare being her sacred animal. Here's another possibility. Ground nesting birds lay eggs in fields, and hares make nests (known as 'forms' or 'scrapes') in fields too. The nests made by the hares look a lot like some bird's nests.
Could it all just be a case of mistaken identity? It's probably not worth investigating too thoroughly... as long as the chocolate eggs keep coming each year. :)