God brought the Israelites across the Jordan river on dry ground. This is a full circle moment for Israel. God brought them out of Egypt by the crossing of the Red Sea. Now it is time to enter the Promised Land by crossing through the waters that have stopped up by God's hands and crossing on dry ground. God was showing them His great power and encouraging them to trust Him as they entered the next phase.
The Israelites were commanded to do something to help them to remember what God has done. They gather stones and set up what we may consider a monument or a memorial (not an idol), 12 stones from the Jordan river one for each tribe. This was meant to be a remembrance of what God did and a conversation starter for kids to ask what they mean. The point is to remember what God has done and tell of His work to the next generation.
God wants us to remember His wonderful works today. He also wants us to tell our kids and grandkids what God has done. Do your kids know your testimony of faith? Do they know the stories of God's faithfulness throughout the history of your family?