Even if the children can see the altar clearly, you'll get nothing but nasty looks and annoyed comments from the people in front, behind, and to both sides of you. A video would be great, though, like the ones the Red Cross uses to teach CPR.
Here’s another idea, we did this in religious ed and the children loved it. One day we took them “behind the scenes” for a tour of the sacristy. The priest explained all the various vessels and things, the closet with all the vestments. This was fascinating to them. We had a “dry Mass” which is where you go thru the prayers and some motions, but it’s not sacramental, there is no consecration (not a real Mass), so that you can stop along the way and explain what the words mean, or what the priest is doing on the altar and why. We had a small group of adults attend, who just wanted to learn more about the Mass.