I think his question is that:
When the gear shifter is in neutral, he can move the gear selector from neutral to reverse or drive without pressing the brake pedal. He is concerned as his children sit in the front seat, and play with the gear selector.
Pretty sure this is normal on a lot of cars
Solution:
Step 1) Discipline your children and teach them the dangers of playing with gear shifter. Or, simply don't let them sit in the front seat.
Step 2) Always put the car in park when stationary or use the handbrake if you need to put it in neutral. There should be no need to put it in neutral really.