You are mixing i-adjective ( _kawaii_ , "cute, lovely") with na-adjective ( _kawaisō_ , "poor, pitiful"). These are simply different, although they share the same etymology. actually meant 'pitiful' in old Japanese, but there was a shift in meaning many years ago.
We say ( _oishi-sō_ , "looks yummy"), ( _tanoshi-sō_ , "looks amusing"), etc., but we don't say to mean "looks cute", because it's confusing. Basically whenever you hear ( _kawaisō_ ), that must mean "poor".
For more information, please refer to this question.