Can you recommend any good "gentle" books (or offer any experience) on middle children? My middle son is 4 and I have a hard time figuring out how to keep things peaceful with him. His behavior ranges from baby-ish to loving/helpful to contrary/exasperating...in moments! Even when I feel like I'm giving him special attention...he seems to randomly test me.

His older brother is 5 and younger brother is 2.5. They all get along great.