Sounds like you did perfect! You called them out the first (and second) time. That is hard to do but it gets them in line before they have a pattern of thinking it is ok.

If your start time is not firm make it known. They might be thinking that since you open at 8am for other kids there is no harm in coming 20minutes early...you are already there working. While this isn't acceptable it is easy enough to see that they could think they way. It is up to you to make it known they can't think this way! Being late on day 1 is a HUGE red flag. You did good.

They may very well turn out to be the best daycare family you have they just need guidance to know what that means on their end. If it continues after you have told them clearly...THEN you have a problem.

Also, as much as your husband may legitimately be concerned that the family will leave if you are firm with them...I think they will find it hard to just up and leave for a new daycare for the hours they are wanting so you can likely be firm and not lose them. Be polite enough about it...but be clear, consistent and firm to ensure they are following the contracted terms.