It's not going to be easy to find a practice area. My Son spent time at BUMPY learning on a TY80 before I bought him an old Amigo and we started going out to trials. We then spent a lot of time between trials at Addingham practicing before we ventured further. Any Child is going to find it difficult at first. After all their are young riders who have been there a year or so and "know the ropes". But if encouraged they will get to the top of the tree. The main thing is to make sure they are enjoying themselves. Also get to the Conducted trials. Barnsley are holding some in Grimethorpe and I have heard good things about them from Ryan Cartwright's parents. Ripon hold some with an "easy" and "Hard" Course held at 3 to 3.30 on the same day as their evening trials. Yeadon Guiseley's hold them at all Centre, Group , club and Beginners trials, the section's are similar at all. Richmond have a conducted or easy course at most of the Youth trials, Horsforth hold some good beginners (at Tong as well!) and contact StuartC at Bradford about His Autotowbars Beginners trials as they also welcome the "small wheelers" and are good at giving them an idea of a "real" trial. The best way to learn is to discover what's out there and ride.
I think I speak for everybody in saying that Kids and Dads are always welcome and all clubs try and make sure that they are going to leave happy after an enjoyable day out.