Answer:
Tension
Step-by-step explanation:
Centripetal force for an object in circular motion. It keeps the revolving object in its path. Centripetal force acts along the radius of the circular path.
It is given by:

where, m is the mass of the object, v is its tangential velocity and r is the radius of the circular orbit.
The source of the centripetal force swinging around in a circle is provided by the tension in the arms of the father holding the child. Weight of the child acts downwards.