As it so happens, even animals as simple as rats have the ability to add quantities smaller than 4 with decent precision. Thus, no rational creature would really think one and two create a quantity as large as twelve (as a result of the distance and magnitude effects). Since Scootaloo is capable of other high functioning activities, this indicates her mistake sprouts from a simple misunderstanding of the base 10 system of representing numbers. No worries, Scoot! (I'm taking a mathematical development seminar against my will and this is the only time I've ever been able to apply it so don't judge me).