Rule reminder
To form a yes/no question with 'avere', use rising intonation with the same word order: 'Hai una penna?' In formal writing, inversion is possible: 'Hai tu una penna?' For information questions: 'Cosa hai?' (what), 'Quanti ne hai?' (how many), 'Chi ha...?' (who has).
How do you ask 'How many children do they have?'