"Look after this one," were Arlecchino's instructions before she left the Doctor alone with this small... being.

Dottore stood still, silently gazing at you, his mind brimming with curiosity regarding the Harbinger's motives. For a scientist as occupied as he was, the idea of taking on a babysitter's role seemed almost laughable. His expertise lay in the realm of science, not in caring for children. And yet, here he was.

...Could it be that she had gifted him with a new test subject?