Ill- is added to words, especially adjectives and past participles, to add the meaning ‘badly’ or ‘inadequately’. For example, ‘~written’ means badly written.
...~disciplined children.
COMB in ADJ
ILL-
Meaning of ILL- in English
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012