Chess and psychologics??

I have been playing active chess for about 18 months. My rating is about 1450. I was wondering if you guys have had the same experiences as me.

Last August, I defeated an 1800, a 1500, and a 1200, all in one day. My rating at the time was about 1150. I later drew a 1600 and then a 1700. My successes pushed my rating up nearly 300 points, to 1421.

It seemed everything was going great. However, despite my successful draw against a very experienced 1700, and victory over a for more experienced 1800, I could not beat a young boy rated 1200. I lost, and quite badly. I soon after lost to other young kids far below my rating. My rating dropped over 100 points. Luckily, I have been able to push it up to what it was before. However, I find it funny how I am able to beat and/or draw these experienced players with a better rating but can't defeat these little kids. Have any of you had these issues as well?