A two month old may try to eat or suck on whatever he is given, but he cannot pick up an object on his own.
I think it likely that a tongue fissure split, causing the cut on the tongue.
It may well be the cause. However, while both of you are using measures of normal development, they are not absolute. An infant instinctively grasps and tries to put what it grasps (usually someone’s finger) into their mouth.
It is conceivable that a two month old would touch and grasp some object that could cause the injury.
However, such an event is unlikely to go unnoticed, the baby immediately screaming in surprise and pain.
Probably a fissure split - but the immediate assumption of parental guilt is what bothers me.
The first assumption should always be that the parents want to care for their child properly; until proven otherwise. Good outcomes are more likely to result from working with the parents under this assumption to correct any problems or deficiencies.
Taking a child away from the parents can be deeply traumatic, and too often it seems to be done in a spirit of governmental self-righteousness instead of a spirit of help.