Simplify the following text for a Grade 10 native English-speaking person.
Original: Jean Piaget ( ; ( 9 August 1896 â `` 16 September 1980 ) was a Swiss developmental psychologist and philosopher known for his epistemological studies with children .
Simplified: Jean Piaget ( 9 August 1896 - 16 September 1980 ) was a Swiss developmental psychologist .