Mosiah 28:6 - 28:10

Mosiah 28:6 And king Mosiah went and inquired of the Lord if he should let his sons go up among the Lamanites to preach the word.

Mosiah then goes to the Lord to see if he should let them go.

Mosiah 28:7 And the Lord said unto Mosiah: Let them go up, for many shall believe on their words, and they shall have eternal life; and I will deliver thy sons out of the hands of the Lamanites.

The Lord tells Mosiah to let them go to preach to the Lamanites. He reassures him that they will be protected and return safely. And because of their desires they are assured of eternal life.
[If I was told that about any of my children, it would be a wonderful bit of news and I would not have to worry as much about having them with me in the next world if I prove faithful.]

Mosiah 28:8 And it came to pass that Mosiah granted that they might go and do according to their request.

So with that reassurance from the Lord, king Mosiah grants leave of his four sons and their companions to go to the Land of Nephi and try to convert the Lamanites to the gospel.

Mosiah 28:9 And they took their journey into the wilderness to go up to preach the word among the Lamanites; and I shall give an account of their proceedings hereafter.

Mormon tells us that he will give a report of their activities later in this book.

Mosiah 28:10 Now king Mosiah had no one to confer the kingdom upon, for there was not any of his sons who would accept of the kingdom.

Meanwhile, Mosiah has no one to give the kingdom to. All of his sons are out on missions to the Lamanites.
[I wonder if he knew whether he would see his sons again. Travel was so difficult and word from the land of Nephi would not be forthcoming. When they left, that would be the last he would either hear of see of them in this life anyway.]