That is very good advice. This afternoon/evening I tried to 'level' with him--got down to his eye level and we talked about why the toys needed to be picked up. We discussed all the things that could happen if the toys are left out (him or someone else getting hurt, toys getting stepped on and broken, losing his favorite cars, etc.). I kept my tone level, but definitive as to not letting him think there was an alternative to doing what I asked...he was still a bit grumpy with his responses, but overall there was no yelling or arguing, and it's now 8:30pm and the toys have since been picked! I think one of the best things I replayed in my mind was about treating him as I would someone else, with a Buddhist mindset. While I will say that it definitely took some focus and a little extra time to talk to him like that, in the end I spent LESS time fighting with him and scolding him into behaving. We even talked about why we shouldn't hit people, and why it's important to speak nicely to everyone-even if they are doing something we don't like.
I'm glad I found this thread and continued to research it. I did find an article online that said the reason there isn't a "Buddhist Parenting Code" or whatever, is because what is right for one child, even in the same family, may not be right for the other child. But that in just making sure that while you are deterring the bad behavior and encouraging good behavior, you keep in mind the Four Truths, The Eightfold Path, and so on. I'm looking forward to less stressful days at home with the kids, and I plan on applying what I've learned daily!
Thank you again!