答案应该是1:1。
随机函数以及精度问题，有点偏差。

Children.java

import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Random;

public class Children {

public static void main(String[] args) {

for (int i = 0; i < 1000; i++) {
new Children().proc(50, 130000);
}

}

public void proc(long birthCount, int familyCount) {

Random random = new Random(System.currentTimeMillis());

List<Family> listFamily = new LinkedList<Family>();

for (int i = 0; i < familyCount; i++) {
listFamily.add(new Family());
}

for (long i = 0; i < birthCount; i++) {

for (Iterator<Family> families = listFamily.iterator(); families.hasNext();) {
Family family = families.next();
family.birth(random.nextBoolean());
}
}

long longGirl = 0;
long longBoy = 0;

for (Iterator<Family> families = listFamily.iterator(); families.hasNext();) {
Family family = families.next();
longGirl += family.girl;
longBoy += family.boy;
}
System.out.println(longGirl + ":" + longBoy);

}

class Family {

public long boy;

public long girl;

public boolean isStop;

public Family() {

boy = 0;
girl = 0;
isStop = false;

}

public void birth(boolean isBoy) {

if (isStop)
return;
if (isBoy) {
boy++;
isStop = true;
} else {
girl++;
}
}
}

}