John Gill Commentary Joshua 4:22

"Then ye shall let your children know, saying, Israel came over this Jordan on dry land." — Joshua 4:22 (ASV)

Then you shall let your children know
The meaning of the erection of these stones, acquaint them with the whole history, the meaning of which they are designed to perpetuate:

saying, Israel came over this Jordan on dry land ;
and if they should ask how that could possibly be done, or if they did not, they were to inform them by what means it was brought about, as follows.