@Vasqueztion Well the real world goes by similar logic. Smaller things are usually weaker. Size is tied to physical ability to a certain degree.
In the world of magic and wonder however there are a lot of extra reasons thats not going to be true. Sure bigger does mean stronger, but as shown it varies greatly between species and such. Its like the Human-Gorilla comparison taken even further.
In this world it seems to have similar logic though they also account for the size of the creatures race. This is after all a baby and relatively weak compared to its older kin.