They're probably eager to let you go & get to their family routine for the evening, so don't expect a full conversation when they come home. Report out to them what they need to know and if they don't have any questions, get on home.
If it's a baby, tell them when the baby last woke up, last ate, and any changes in behavior from the day, plus an cute moments the parents would appreciate. If it's an old kid, let them know the status on homework, when the kid had dinner, any messages the school wanted conveyed, etc.