Celestia and Philomena a hit by a age spell and both be go back as their baby timeline and is not easy to be with the mind as a full grown mare in the body of a baby, cadence to care of Celestia the time Twilight found the spell to turn back to normal but Philomena ajoy it! Cadence too a be hit,and go back as her teenage timeline, Luna a not be hit but now she must do the job of sister to make sure equestria not fall apart, the girls help Twilight to found the Spell in the old castle of the two royal sister. Discord him look for who a done this and give him a challenge to found but thanks the fact he can feel magic is what help him to found where the criminal hide or run away, Shining and flash sentry do their the royal guard duty!

Lol

I read a fanfic just like this.

slightly dodgy english aside,  
this is cute

is that princess celestia in the highchair

De-aging spells suck for all parties involved.

Age regression and bad grammar.

Age regression, or is Cadence an old lady?
 
Wait, no, it’s age regression.