Training once or twice a week is plenty, and should not last longer than one hour and fifteen minutes. Learning how to control it should be the main objective. They need to touch it as many times as possible during fun activities that will engage them. Challenge them to get better by practicing on their own. There is no rule which states that they can't learn by themselves, no matter how important we think we are.
Incidental things are important.
They are forming the habits that will impact their future participation. Realize, however, that they often forget and will need to be reminded often. Ask them to work with others to solve a particular challenge. Start them with just one partner and work from there. A brief warm-up is appropriate in order to get the players thinking about soccer and to prepare them physically for the time ahead.