The first thing that comes to my mind Dimitri – is “Don’t do it”. I only say that due to the fact I have one in my own helmet and it is rare, very rare, that it has ever helped me in any way. Rarely does it even get used anymore. Yes, it has come in handy a time or two, but in most cases, last thing I want when focused on driving (which your boys should be) is someone talking in my ear.
Not sure how old your boys are, but communications in a helmet definitely have a tendency to distract a driver, particularly the younger ones. I would think a one on one “pit talk” after on track sessions would be of much better benefit to you and your boys than a radio will ever be.
Just my two cents…
But hey, if you want to give it a try – go cheap! You can get a system which uses the simple two way handheld radios, much like the ones they use on motocycles. Look at “Rugged Radios” dot com.
We may not be the fastest on the track...but we're having the most fun!