@book{GesellIlg, author = {Gesell, A. and Ilg, F. L.}, title = {The child from five to ten, New York (Harper \& Brothers) 1946.}, language = {en} } @book{IlgAmes, author = {Ilg, F. L. and Ames, L. B.}, title = {Child behaviour, New York (Harper \& Brothers), 1955.}, language = {en} }