Exodus 12:26

And it shall come to pass, when your children shall say unto you, What mean ye by this service?

It will happen, when your children ask you, 'What do you mean by this service?'

And it shall come to pass, when your children shall say unto you, What mean ye by this service?

and it hath come to pass when your sons say unto you, What `is' this service ye have?

When your children ask you, ‘What does this service mean to you?’