回複：回複：180 day is determined by the time they leave

1. Yes, and if their previous status is H, they should have 10 days as grace time (some times VO won't count it). Anyway, they are within the 180 days mark.
2. I do not know what xiaobaitu means. My opinion, leave the applicaiton alone. If the application is eventially approved, there will be no (or a much short) overstay period for your LG and children.

Good luck to your LG and children's visa application in the future. It is not unusuall to forget extending status of the H4 holders. They will be fine at visa application. I think that it may help securing a letter from your lawyer stating the fact that he forgot doing the extension.