This was a cruel thing to do, as cats [and dogs] use their whiskers for a lot of sensory info.
Short answer, YES, they will grow back BUT it will take awhile, & for all of that time your kitty is not safe outdoors.
They are at some risk indoors too, but less so, because if they get stuck, you are more likely to hear them crying, & rescue them.
Until the whiskers are all grown back, your cat can't be allowed to go outside; they use them to decide if a space is big enough to get into/out of, & can be easily trapped and die if not quickly extracted.
Please tell your son that this was a "haircut" that the cat didn't need, and was very distressing to them. Cats with their whiskers cut have trouble drinking water - they snort it, up their nose, because they get too close. They stumble, look drunk, & seem disoriented - it's terrifying for them, & they may scratch or bite, in their fright.