They grow up so fast

Yeah after seeing the episode I’m not 100% convinced. In this comparison Rarity is stretching vertically in the sisterhooves social pic, while the sitting models are pretty rarely used and introduce more opportunity for inconsistency.
 
I just surveyed about a dozen pics from S1 to S7, measuring from hoof-bottom to ear tip of similar poses between CMC and adults in the same scene. S1 to S6 the CMC are pretty consistently between 65% and 75% the height of an adult.
 
Here’s some season 7 pics:  
 
 

 
In some season 7 pics, CMC look to be about 85% the height of the adults, but then there’s:
 

 
Here Scootaloo is about 54% Cheerilee’s height, hoof to ear tip.
 
Need more data

One of the most defining moments for me of her growing up was when she ordered a salad instead of ice cream. Our growing young mare’s gotta keep up that perfect figure!

I’m not looking too deep into it. The size of the flash models have always been a bit inconsistent (just look at Dragon Lord Torch or Big Mac on a subtler scale), and the characters have always been as big as they need to be. In this case, Sweetie needed to be able to reach the counter.

They grow up so fast.

Spike’s turn when?

Awwwwww, look at our cute little unicorn blossoming slowly into a strong and healthy mare like her sis…

Aww shes growing up so fast :’)

@ArrJaySketch  
plus their voices are noticably deeper

I’m more interested in Rarity’s progress in her relationship with her sibling

I’m pretty sure the CMC are growing up. I remember seeing another comparison pic of them standing, somewhere.
 
I want to keep an eye out for this!

Well damn she grew a neck! First a tribe stamp then they try to take over Equestria…

@Lobinchi  
I’d like to believe they are, but I can’t help being skeptical on the matter. I’d really love to see the cmc’s models change subtly as the show goes on… it would certainly help sell Sweetie Belle’s changing voice.

@ZONESS  
No, stop imagining stuff and creating theories, they’re growing TwT  

I’m not convinced this is intentional, personally. I’m more inclined to believe the animators mess with the scale of the flash models constantly to create a sense of perspective and a side effect of that is the characters being subtly inconsistent in size episode to episode. I’m not saying it couldn’t be intentional, it’s just not my first instinct to assume that’s the case here.

Yoo that’s crazy man

I’d like to imagine the CMC as around 10-12 at the start of the series with them being 15-16ish as of now.

 
Th-they really are growing up, aren’t they?

L-liquid pride… Liquid pride QwQ  

Getting your butt tattoo kind of helps.

Kinda hard to gauge since one of the shots has them both sitting down, while the other is them standing up.

oh shit she has
 

Our mini marshmallow is growing up…