The Chamber of Infants is the same of Pantheon of the Kings;
Most of the Infantes and Infantas of Spain are burried in the Chamber of Infants. Also it is destinated to Queens of Spain that weren't mothers of Kings.
The Pantheon was built in times of Queen Isabel II, it is composed of 9 chambers with a total of 60 niches (tombs), currently just 36 tombs are engaged .The picture you refer is a beautiful mausoleum located in the 6 chamber.
Here you are some practical info: