We're not having the discussion about yukkuri body mass again, are we?
Let's say the mother can be conformed to a sphere of 15in diameter, or 0.381m diameter and 0.1905m radius. The volume of such a space would be 0.029m^3, or 29000cm^3.
As a control experiment, if we assume this space is filled with water (1g/cm^3), then the yukkuri would weigh 29000g or 64 pounds.
His center of balance is wrong. You can push Michael Jordan over with your finger tips under the right circumstance. It looks like the mother has just enough strength to push one leg into the other and tangle his balance.