I always wanted to make PokeyPie offspring, but I never had proper idea for them XD But, now I’ll give it a try:
 
Name: Marshall Royal Pierce(Marshmellow for practically everyone, what drives him mad)
 
Parents: Pinkie Pie and Pokey Pierce
 
Siblings: Twin brother- Pickaxe
 
Type: Earth Pony
 
Occupation: Baker
 
Personality: Mean, grumpy, sarcasstic, responsible
 
Marshmallow is a hardworking, busy colt with reluctance to other ponies. Ponies says that he used to be really cheerful kid in a duet of party planners with his twin brother, however Pickaxe found his new passion (mining) and moved out to a rock farm. Without his brother, Marshmallow became kinda lost, and having a “blank flank”didn’t help him too much to get friends. And with constant companion of his too cheerful mother, he turned out to be a grumpy baker.  
Despite his difficult character and how much she has been irritating him, Marshall loves his mother and tries to take care of her with her silly ideas. He’s a very good baker but he hates when someones interrupts him.
 
Extra:
 
-He’s afraid of dark, that’s why he couldn’t acompany his brother in mine.
 
-He’s good at magic tricks.
 
-Can brake 4th wall like his mother.
 
-His parents from father’s side lives in Canterlot.
 
-He loves his apron.