Your toddler might be realising the reflection in the mirror is them, and this is thought to show that their self-awareness is developing. The experiment that shows this involves putting a dot on a child’s face without them noticing. If they touch their face when they look in the mirror, it is thought that they understand that the reflection is them.
Scientists tried the same experiment with three Asian elephants, and one elephant touched the mark with her trunk on the first day of marking. The researchers believe this shows that elephants have the capacity to recognise themselves in the mirror.
Reference:
Plotnik, J.M, de Waal, B.M. & Reiss, D. (2006). Self-recognition in an Asian elephant. Proceedings of the National Academy of Sciences, 103(45), pp. 17053-17057.