There are so many differences between girls and boys. First of all, their bodies will develop differently when they grow up depending on their sex. Their sexual organs will also be different from each other. The dominant hormones in their systems will not be the same too although there are some cases wherein the hormones that are dominant in their systems are not the ones that are expected.
The strengths and weaknesses of boys and girls are also a bit different. For the longest time, men dominated the world until they have realized that actually, there are certain things that they cannot do without women. These two sexes would need to work with each other to reach the type of world that will be ideal and conducive for both of them.