If you do not measure how they spend their time in any way, you can not expect to handle them properly. Ask them to fill in the old time sheets to find out.
Divide the timesheets into two aligned columns, one covering the 15-minute interval of the work day, and the second column leaving a margin to say what they were doing for that period. Timesheets are easy to do. They will hate this, but they will soon get used to filling them. Tell your staff that this is a productivity and time management exercise and run it for at least a month. If you find that it works well, extend it. Make sure their names are on them and save them for later review.
It's a very useful thing to do. I have already done this with the staff before and if nothing else focuses attention on the time lost. It also shows the tasks that are wasting a lot of time and gives you and your team the opportunity to think about how to make the processes faster while remaining effective. The whole exercise must be presented to them in a positive light. At the end of the day, you will make their life easier too.
You can also watch each of them for a day or two and find out exactly what they are doing. The more you understand their work and the obstacles they face in their daily work, the better you will be a boss. Your staff will also be happier that you are interested in their individual roles. Be open to suggestions for improvement and discussion during these ghost sessions. You will be surprised at the number of good ideas that emerge when people have the opportunity to sit alone with you.
You are the boss so take control! It's your responsibility to lead and give the example. Not knowing what they do all day is not a good example. You can handle them much better after that, I guarantee it.