Read the passage given below and answer the questions that follow: (121-128)

A couple of days later, there was a music recital in the Bharatendu Auditorium, one of the two largest auditoriums in town. One of the performers was Ustad Majeed Khan.

Lata and Malati both managed to get tickets. So did Hema, a tall, thin and high-spirited friend of theirs who lived with innumerable cousins–boys and girls–in a house not far from Nabiganj. They were all under the care of a strict elder member of the family who was referred to by everyone as Tauji.

Hema’s Tauji had quite a job on his hands, as he was not only responsible for the well-being and reputation of the girls of the family but also had to make sure that the boys did not get into the countless kinds of mischief that boys are prone to. He had often cursed his luck that he was the sole representative in a university town of a large and far-flung family. He had on occasions threatened to send everyone straight back home when they had caused him more trouble than he could bear. But his wife, Taiji to everyone, thought she herself had been brought up with almost no liberty or latitude, felt it was a great pity that her nieces and grandnieces should be similarly constrained. She managed to obtain for the girls what they could not obtain by a more direct approach.

This evening Hema and her cousin had thus succeeded in reserving the use of Tauji’s large maroon Packard car and went around town collecting their friends for the concert. No sooner was Tauji out of sight than they had entirely forgotten his outraged parting comment. “Flowers? Flowers in your hair? Rushing off in exam time- and listening to all this pleasure - music! Everyone will think you are completely dissolute–you will never get married.”

What does the underlined expression 'the boys are prone to' mean ?