Mahler wanted to observe the real-time interaction of mothers and babies during the first three years of life. She set up a laboratory, which eventually expanded to several adjacent rooms. There were areas with chairs for the mothers to sit comfortably. There were also rooms full of toys. This gave the babies the choice either to be close to their mothers or to separate from them in order to explore the rooms full of toys. The systematic observation of mothers and babies began when the babies were about four or five months old. Mahler assumed that the separation-individuation process did not start until this age.