This strip is adapted from the Li'l Folks comic strip from January 9, 1949:
Is "Sparky" a pseudonym used by Schulz?
Yep!
His uncle called him "Sparky" after the horse Spark Plug in Billy DeBeck's comic strip Barney Google, which Schulz enjoyed reading.
Doesn't say why he started using his real name with Peanuts, though
For posts about the comic Peanuts, by Charles M. Schulz
This strip is adapted from the Li'l Folks comic strip from January 9, 1949:
Is "Sparky" a pseudonym used by Schulz?
Yep!
Doesn't say why he started using his real name with Peanuts, though