Or HaChaim on Deuteronomy 5:1/אור החיים על דברים ה׳:א׳

1 ויקרא משה, Moses called, etc. It is conceivable that as a result of the conquest of the lands of Sichon and Og the Israelites were scattered over a large area at that time. This made it necessary for Moses to call them together. Alternatively, up until this point Moses had addressed only the men; now that he wanted to review the Ten Commandments he made sure that everybody would be present. At the original revelation the entire nation including children had also been present.