You can get there by going through the animation show, but if you don't want to do that, you can also walk in through the Animation Gallery store.
This is not rue any more. Once upon a time guests entered via the gift shop to go directly to the animation class. Now you are supposed to go through the front of the attraction. You can still bypass the animation tour/show, but they want guests to go through a turnstile- more or less. Often a CM is posted in the gift shop to prevent guests from going that way.
The animation class has indeed become more popular over the years.
If you wish to go, I suggest arriving 'early'. Shows run every half hour much of the day, but they do get full. You can no longer show up at 1:50 and expect to get into the 2pm show, especially if you don't want to be a 'lap' person. (a person who has to hold a drawing board on their lap)
There is no age restriction for the show, but the seats are kind of odd swivel seats, and the class might be a bit long for kids under age 5. Very small kids might not be able to sit on the swivel seats, since they don't have a back and they swivel. (a bit like sitting on an old fashioned lunch counter stool). If you have a child near that age, you may actually wish to sit in the 'lap' table seats and share a board. Those are more like bench seats.
Then again...if you have a small child, understand the show is 30minutes of sitting quietly. They may not have the patience to follow directions that long. They must be quiet or the class will be ruined for
everyone else. I've been there when someone was coughing, or a child was loud...if everyone else can't hear the instructor, then they don't get to finish their drawings. It's not fair to everyone else in the room to bringa disruptive child.
Right next door to the animation class is Playhouse Disney, and voyage of the Little Mermaid...if you plan ahead, it's not hard to do a spliit deployment.