Ok, I'll bite.
I guess the App is better than hitchhiking (which in my opinion is extremely dangerous both for the passenger (the driver can turn out to be a criminal)
And do what? As a hitchhiker you're asking a random person for a lift, which is statistically very safe indeed. The probability that a randomly selected person stopping his/her car is not only a criminal but a criminal who would target you is very small indeed.
It's like asking someone to watch your laptop for a while in Starbucks while you go to the toilet. If you ask a random person, chances are you're ok. If someone offers to do it, be wary.
and the driver (the passenger could turn out to be a criminal).
If this were true, cab driver would be a seriously dangerous job. In most countries, it isn't. I concede that in countries where hitchhiking has become less common, there's probably some cause to exercise caution regarding whom you might pick up. Common sense goes a long way.
Please, enough of the fearmongering. The western world is a safe place. You'll be fine, and so will your kids.