Albert Barnes Commentary Exodus 10:24

"And Pharaoh called unto Moses, and said, Go ye, serve Jehovah; only let your flocks and your herds be stayed: let your little ones also go with you." — Exodus 10:24 (ASV)

Your flocks and your herds - Pharaoh still exacts what would of course be a complete security for their return: but the demand was wholly incompatible with the object assigned for the journey into the wilderness.