Most of our children aren't called to conquer lands through combat like Joshua did when he claimed the promised land. While victory was assured if Joshua would believe God and go, casualties and blood were likely. God's direction in Joshua 1 to have strength and courage made sense when fighting armies.
But, our children are more likely to face business decisions, angry people, and nagging questions of insecurity. The same types of problems that Solomon met when he tried to build the temple. His battles and fears were like those our children will meet.
The solution is the same. To fulfill God's purposes and to have success, strength and courage are needed in business as well as battle. David tells Solomon in 1 Chronicles 22:13: "Then you will prosper, if you are careful to observe the statues and the ordinances which the LORD commanded Moses concerning Israel. Be strong and courageous, do not fear nor be dismayed."
Even though Solomon had 100,000 talents of gold, 1,000,000 talents of silver, and practically every other resource imaginable, David knew that his son would need to follow God and have strength and courage. David knew that being king and having wealth weren't enough, fears and lost hearts are inherent in any endeavor worth pursuing. Solomon, like our children, was in danger. Solomon needed to be a braveheart to build God's house, just as our children need to be bravehearts to build their lives.