I agree. Wet saddleblankets, plenty of miles and varied experiences are the ONLY things that make a truly bombproof horse.
Absolutely. Working in a pen/ring with spooky stuff does help, but cannot replace actually being on the trail without the security and familiarity of 'home'.
If you have a seasoned trail horse available, riding with or ponying with a seasoned trail horse works wonders for young ones.
Also, as you're working/training your horse, something you may want to keep in mind....in my experience being a bombproof trail horse and being a good lesson horse (especially for children) require different skills/experience/disposition from your horse.
Some horses actually love children for some reason and are very tolerant and forgiving
with a child rider. Our mare, Lady, is like this... she's is a very good, reliable, trail horse (almost bombproof, just needs more miles), but had been started as a lesson horse at 3 yrs because of her disposition with children.
On the other hand, our lead mare, Angel, is a seasoned, bombproof, ex-penner that will do anything and go anywhere you want, but...because of her experience and training, she is very
light in the mouth and with the leg. She is tolerant and works great as a lesson horse, too, but is a much better match with a more experienced rider than you usually see in a child.