“ For YHWH your God dried up the waters of Jordan from before you, until you were passed over, as YHWH your God did to the Sea of Reeds, which he dried up from before us, until we were passed over.”
Note the change of pronoun to ‘us'. Joshua had been present at the crossing of the Sea of Reeds when they left Egypt, and he now likened the two events. The same God had taken them through the waters then and had brought them through the waters now. He was the same God as the Great Deliverer from Egypt. The two events were constantly linked together in the people's worship of God (see Psalms 114).
These words are not part of what is to be specifically said to the children although no doubt the gist of them would be conveyed, for, had they been, the same pronouns would have been used throughout.