Because I'm guessing that his children either respected or feared him enough to not misbehave, I'm guessing that Trump cannot understand or relate to what follows that nearly every family knows all too well and especially how it relates to ISIS.
If you ask any couple that has an infant who frequently cries and screams and is inconsolable, who is the most powerful person in their family, they will tell you, it's that infant.
Why? That screaming infant can cause a mom or dad to swerve dangerously across lanes, can end a meal at a restaurant and sometimes even stop a vacation dead in its tracks. To make matters worse, not only can't the parents silence such a child, but any irritated onlookers at neighboring tables will only make that infant scream louder if they try to interfere.
What does this have to do with ISIS and Trump?
Consider for a moment that the recruits who are drawn and seduced by the Siren's call of ISIS are the equivalent of those screaming infants, except their screaming goes on inside their imaginations with regard to their anger at their peers, community, school and life. And then they become mesmerized by the promises of an extremist group to love them, take care of them, value them, provide them with sex slaves and then instead of quieting them, to train them to get even with the world they are so angry at. Best of all, if they die for the cause, it gets even better and they get to go to paradise.
If Trump or even Cruz thinks it is simply a matter of smashing ISIS or whatever other extremist group takes its place, they are thinking they'd have much better luck than parents of screaming infants.
They are also ignoring what worries many anti-terrorist experts which is that the recruiting then radicalizing of these impressionable, disaffected young males and then the sending them back to their countries of origin to commit jihad is a much more difficult enemy to defeat than an armed state.
In fact, threats by Trump or Cruz (to carpet bomb), if anything might even incite the development and spread of more extremist groups. Just as ISIS has superceded Al Quaeda, if ISIS is defeated, another group will follow it. You can't eliminate evil or the thirst for power by evil people through radicalizing impressionable youth to carry out their evil deeds.
In the long term the only real approach is to identify vulnerable, impressionable, frustrated and hurt young males before their frustration and hurt crosses over into wanting to retaliate and seek revenge.
To do that would require a complete paradigm shift to thinking preventively instead of being in denial or minimizing the problem and then reacting when it suddenly explodes a la waging the war in Iraq after 9/11. By then the cows have left the barn.
It's analogous to how preposterous it is to think you could eliminate all the cockroaches and vermin in all the restaurants and marketplaces in the world, when the only approach is to keep such places clean enough so that such pests never get the chance to breed.
Likewise, only when we can intervene early with young male youth before their frustration turns to hatred do we have a chance to prevent evil breeding within and among them.