Leaping babies

Question: 

Whose baby "leapt in the womb" when her cousin Mary came to visit her?

Bonus:  Who was that child?

Painting of Mary visiting Elizabeth by Carl Bloch
Answer: 

Elizabeth.

Luke tells the story of Mary's visit to her relative Elizabeth in Luke 1:39-45.

Bonus:  That child was John the Baptist

Above is a painting of the visit by Carl Bloch.  Notice how old Elizabeth looks--well beyond child-bearing years.  The angel Gabriel, when he tells Mary that she is to bear a son, also tells Mary that Elizabeth is pregnant "in her old age."  This is found in Luke 1:36.  Only Luke tells us about Mary's visit to Elizabeth.