When the girls got there, Canterlot was a mess.
Harmony gasped. “Who would do such a thing?”
Suddenly, Princess Celestia and her younger sister, Princess Luna, walked up to the six.
“Are you six alright?” Luna asked.
“Yeah, we’re fine,” Colorful answered.
Suddenly Celestia gasped. “Sister, these aren’t just any fillies. They're Rainbow Dash, Pinkie Pie, Rarity, Queen Twilight Sparkle, Applejack, and Fluttershy’s children!” she said.
“Oh, we must get them inside!” Luna said as she grabbed Colorful, Sugar, and Diamond. Celestia grabbed Firework, Cider, and Harmony.
The princesses took the girls to the castle.
“You six must stay here until further notice,” Celestia insisted.
“But why?” Colorful inquired.
“Queen Chrysalis’ daughter, Princess Cocoon, sent her Changeling minions here and they destroyed Canterlot. It’ll be repaired, but we have reports that the Changelings are still out there. We sent all the ponies in Canterlot here until further notice.” Luna explained.
“We can help! Our moms saved Equestria for years!” Sugar said.
“I don’t know. You girls are still children.” Celestia thought about it.
“We’ll whip Changeling flank even if it’s risky!” Colorful declared.
The princesses sighed. “Okay. But the Royal Guards will keep watch of you.” Celestia gave in.
The six cheered as they left.
As the girls stepped out, the Changelings appeared. They took form of the fillies. The real six were frightened, but they fought as well as ever. They stuck together and fought with their own weapons.
Colorful flew up and kicked their flank.
Sugar got out a “party cannon” and fired it at them.
Diamond got out a bottle of Fiery Fabulousity Hairspray, a type of hairspray that her mother created, and shot it in their eyes.
Firework used her Alicorn magic to bounce them away.
Cider brought out apples and kicked them at them.
Harmony used her singing voice to almost rupture their ear drums, even though she was a talented singer.
After several minutes of it, the Changelings surrendered the battle. The citizens of Canterlot came out of the castle.
“Oh, thank you girls!” Celestia thanked.
“You’re welcome, Your Majesties,” Diamond curtsied. The other five did the same.
“Would you girls like to come to the 15th Annual Royal Dinner? As a thank you gift?” Luna offered.
“No, thank you. We have some business to take care of.” Harmony politely rejected.
After a hearty goodbye, the girls took off.
“Next stop: Macintosh Mountains,” Firework said, checking Canterlot off of the map.
5712934
You're making no sense to me.
5713251
You made this too fast and straight forward, the way you described this chapter was 'they came, insulted each other, beat up a bunch of changelings, then left'
Basically, you are missing a LOT of detail, with several plot holes as well. They hate each other, don't they? So, that would mean that the only reason they work together is because their parents are in danger, therefore it would be too easy to have them be tangled up in their own hatred and spite and mess up. This is a good idea for a story, it's just really short and has a couple of plot holes and questions in it. No offense.
From what it seems (and from what I understand) you're focusing on either that they hate each other or that changelings are the antagonist, not much of both.
Now keep in mind that I am not a professional reviewer and I most likely overlooked and/or misunderstood some things, but like I said, this is a good idea, it's just lacking in details, I can help you if you want.
5713377
Oh, okay! Thanks for the advice! I'll try to fill in some plot holes in the next chapter!