If it is a normal Sunday Low Mass without Benediction of the Blessed Sacrament, look at about an hour to an hour and ten minutes or so. With Benediction add another twenty minutes. For a High Mass look at about an hour and a half or so. If it is a Solemn High Mass it could go one and a half to two hours.
Most women do cover their heads with either veils, scarves or hats or some sort. Berets seem a particular favorite of the younger women at our Mass. As far as little girls I don’t really think there is any set rule, not there is a rule about women covering their heads either, but from what I have seen if the child receives communion normally the head is covered. I would say at the Masses I’ve been to, maybe 90% of the women cover their heads, so I really wouldn’t worry too much about that…
There is a lot of kneeling, which is hard for some people to do. I notice that those unable to usually sit or stand as the case may be.
Don’t get wrapped up in trying to use the Missal. It can get confusing . Most good Missals, St. Joseph, St. Andrews etc, have everything in Latin and English. Most places where they have the Mass also have small red booklets, misallettes I guess which describes everything pretty well. I actually hope it is a High Mass with Benediction. They are very very beautiful, reverent and an incredible experience.
I can only echo the previous poster in saying, experience the Mass. It will somehow, someway join with you and lift you. It is very hard to explain, At times the silences can be overpowering, and the reverence awe inspiring.
I truly hope that the experience is a good one for you and your family. When I first returned to the Traditional Mass, it actually had me crying about halfway through. I had forgotten just how beautiful it was.