This is a great question! I'll share with you some differences I've found between boys and girls who are about the same ages as the boys in the novel. Remember that these are generalizations of boys and girls who are ages eight to about twelve. It's not unusual for girls to be tomboys at this age, displaying many characteristics typical of boys.
It's been found that in almost every culture, boys are more aggressive than girls. Boys spend time playing competitive games, so focused on the rules that they often argue with their friends about them. ("You broke the rules!") Girls are more likely to settle their differences by talking them out. Instead of arguing about the rules, they'll usually suggest a compromise of some sort to either change the rules or change the game they're playing. Girls also tend to play games that involve taking turns so everyone gets a chance to play.
Boys are also sometimes encouraged to be assertive and outspoken. They're very physical at this age, wrestling and playing roughly, to prove who is stronger, faster, etc. They have lots of energy, seeming to be tireless. Girls tend not to be as assertive as boys in this age group, but they can be outspoken and noisy. Their games aren't as physical on the whole. Girls don't feel the need yet to outdo each other, but they definitely are as energetic as boys at this age.
The age group is what's important here. As teenagers, things change. I hope this helps.