John Gill Commentary Joshua 4:21

"And he spake unto the children of Israel, saying, When your children shall ask their fathers in time to come, saying, What mean these stones?" — Joshua 4:21 (ASV)

And he spoke unto the children of Israel, saying
At the same time he set up the stones:

when you children shall ask their fathers in time to come, saying ,
What [mean] these stones? (See Gill on Joshua 4:6).