Mother and child by Jay-Co
Pygmy Marmoset or Dwarf Monkey (Callithrix pygmaea) is a New World monkey species native to Bolivia, Brazil, Colombia, Ecuador, and Peru.
Pygmy marmosets are the smallest extant monkeys, with an average body length of 13 cm. A coat of buff and grey fur is marked by yellow, green, and/or black ticking on the head and back.
Source and more information