I've raised two sons, now 12 & 25. Our closets and garage have dozens of toy guns. My 4 YO grandson loves playing with them, as well as playing Angry Birds, watching Paw Patrol ("Chase is on the case!"), and he just finished up his first season of T-ball.
What I see described is not “pretend violence” so much as it is a boy acting in his role of protecting the weak from bad guys.
Bad guys will use violence, so a normal boy is wired to know that he’ll have to respond in kind.
We saw this in “Christmas Story” with Ralphie’s fantasy of protecting the family from Black Bart’s gang.