This isn’t exactly how it happened but Veggie Tales does a good job of giving you the important details of Joshua leading the people to the Promise Land and Jericho. Now read how it really happened.
Joshua 5
13And then this, while Joshua was there near Jericho: He looked up and saw right in front of him a man standing, holding his drawn sword. Joshua stepped up to him and said, “Whose side are you on—ours or our enemies’?”
14He said, “Neither. I’m commander of God’s army. I’ve just arrived.” Joshua fell, face to the ground, and worshiped. He asked, “What orders does my Master have for his servant?”
15God’s army commander ordered Joshua, “Take your sandals off your feet. The place you are standing is holy.”
Joshua did it.
Joshua 6
1Jericho was shut up tight as a drum because of the People of Israel: no one going in, no one coming out.
2-5God spoke to Joshua, “Look sharp now. I’ve already given Jericho to you, along with its king and its crack troops. Here’s what you are to do: March around the city, all your soldiers. Circle the city once. Repeat this for six days. Have seven priests carry seven ram’s horn trumpets in front of the Chest. On the seventh day march around the city seven times, the priests blowing away on the trumpets. And then, a long blast on the ram’s horn—when you hear that, all the people are to shout at the top of their lungs. The city wall will collapse at once. All the people are to enter, every man straight on in.”
6So Joshua son of Nun called the priests and told them, “Take up the Chest of the Covenant. Seven priests are to carry seven ram’s horn trumpets leading God’s Chest.”
7Then he told the people, “Set out! March around the city. Have the armed guard march before the Chest of God.”
8-9And it happened. Joshua spoke, the people moved: Seven priests with their seven ram’s horn trumpets set out before God. They blew the trumpets, leading God’s Chest of the Covenant. The armed guard marched ahead of the trumpet-blowing priests; the rear guard was marching after the Chest, marching and blowing their trumpets.
10Joshua had given orders to the people, “Don’t shout. In fact, don’t even speak—not so much as a whisper until you hear me say, ‘Shout!’—then shout away!”
11-13He sent the Chest of God on its way around the city. It circled once, came back to camp, and stayed for the night. Joshua was up early the next morning and the priests took up the Chest of God. The seven priests carrying the seven ram’s horn trumpets marched before the Chest of God, marching and blowing the trumpets, with the armed guard marching before and the rear guard marching after. Marching and blowing of trumpets!
14On the second day they again circled the city once and returned to camp. They did this six days.
15-17When the seventh day came, they got up early and marched around the city this same way but seven times—yes, this day they circled the city seven times. On the seventh time around the priests blew the trumpets and Joshua signaled the people, “Shout!—God has given you the city! The city and everything in it is under a holy curse and offered up to God.
20The priests blew the trumpets.
When the people heard the blast of the trumpets, they gave a thunderclap shout. The wall fell at once. The people rushed straight into the city and took it.
21They put everything in the city under the holy curse, killing man and woman, young and old, ox and sheep and donkey.
Response: Why do you think God ordered them to kill everything in the city? (Actually, a harlot named Rehab and her entire family were spared because she helped two spies escape earlier and made a deal with them to let her and her family live when they took over the city. We will discuss this more on Sunday.)
Haygood Youth Ministry 
So that only the Israelites would be in the promise land.
Want isarel to get to the promise land
I think God ordered them to kill everything in the city so the Israelites could get to the promise land.