Pinkie Pie is taller because of her heels! Well, that or Sonata looks smaller because of her pose.
 
Info:
 
First Child:
 
Name: Helena Pie  
Nickname: Lena, Sugar Pie(by her mom, Pinkie)  
Gender: Female
 
Second Child:
 
Name: Levana Pie  
Nickname: Lemon (cause of her sour attitude…), Lev  
Gender: Female
 
all bases by: Digital Series Pinkie Pie Baseby SelenaEdeEquestria Girls Pinkie Pie Base 04by SelenaEdeEquestria Girls Sonata Dusk Base 04by SelenaEde Equestria Girls Sonata Dusk Base 03by SelenaEde Helena and Levana belong to me(so don’t steal)  
Pinkie Pie and Sonata belong to: Lauren Faust and Hasbro  
Mlp Friendship is Magic belongs to: Lauren Faust and Hasbro  
Mlp Equestria Girls belongs to: Lauren Faust and Hasbro