Near the end of the 19th century, newspapers began to encourage children to send letters to Santa Claus at their addresses, so they could print the best ones. Older children learned to write letters, and little ones as young as three would dictate letters to let Santa know what they'd like for Christmas. Some were straightforward lists of toys, and others poured out their hearts to St. Nick. There are a few rascals, too, such as the child who let Santa know he broke all of last year's toys. In 1907, Percy from West Virginia was obviously prompted to remember his sisters, although he didn't really care about what they received. Maxwell in Florida, on the other hand, was genuinely concerned about his neighbors in 1915.
Read 23 such letters to Santa from as far back as 1896, at mental_floss.