Is it me, or my 450D? Focussing and image quality

JFLy wrote:

My first post to the forum but have done a lot of research here over the years.

I've had my 450D for 4 years. I have the 18-55mm kit lens and the EF 50mm f/1.8 II.

I'm a keen enthusiast, concentrating on outdoor child and family portraiture. I would like to take my photography to the next level, but am frustrated by out of focus images. I get better results when I only have one subject to contend with, but if it's 2 or more people, all bets are off. Some sessions I've come out with at most 10% of images that are sharp enough to warrant post production. Not good enough.

I don't use a tripod as I'm always running around after the subjects. I have tried MF with mixed results - better with the 50mm. I have tried the different AF settings, and today I had a disastrous shoot with Servo. I have tried increasing shutter speed to "catch" the subtle movements of toddlers. I increase ISO to give me more play with aperture/shutter speed. All in the pursuit of sharper images.

I am sure that my camera can take "good enough" shots, when the planets align. But what more can I do? Uprgrade my camera so I have more focussing points? Full frame? Faster lenses? Go back to the basics and go on a course? Stop shooting fidgety children?

I appreciate any suggestions on how to improve.