Why Children Born in the Wilderness were Circumcised

Joshua 5:4-9

4  And this is the cause why Joshua did circumcise: All the people that came out of Egypt, that were males, even all the men of war, died in the wilderness by the way, after they came out of Egypt.
5  Now all the people that came out were circumcised: but all the people that were born in the wilderness by the way as they came forth out of Egypt, them they had not circumcised.
6  For the children of Israel walked forty years in the wilderness, till all the people that were men of war, which came out of Egypt, were consumed, because they obeyed not the voice of the LORD: unto whom the LORD sware that he would not shew them the land, which the LORD sware unto their fathers that he would give us, a land that floweth with milk and honey.
7  And their children, whom he raised up in their stead, them Joshua circumcised: for they were uncircumcised, because they had not circumcised them by the way.
8  And it came to pass, when they had done circumcising all the people, that they abode in their places in the camp, till they were whole.
9  And the LORD said unto Joshua, This day have I rolled away the reproach of Egypt from off you. Wherefore the name of the place is called Gilgal unto this day.