Camera Upgrade Question

[mikeficklonni]

Full disclosure, I know very little about cameras.  We currently own a Canon EOS Rebel XSI.  We have the lens that came with the camera back in 2008, EFS 18-55mm, and purchased a Sigma 18-300 F3.f-6.3 Contemporary DC Macro OS HMS Lens (purchased 2013).  

Typical usage is kid's soccer games, special occasions, vacations / maybe landscapes...etc.  Looking for quality pictures and possibly fast-moving action shots.  The camera is old and the picture quality is poor.  (Could be user error.) 

Anyway, we would like to upgrade to a Canon EOS 90 D (unless someone recommends something different).

Since we have the above-mentioned lens, should we purchase the body only?  Is the 90D standard lens much better than what we currently own?  I don’t know how good our Sigma lens is in comparison to newer lenses.  I've read that my current lenses are compatible, but with the upgraded camera should we upgrade our lens or go with the body only?

We appreciate all advice.

Thanks in advance.

Mike

[ebiggs1]

My preference would be the Canon or the Sigma 18-35mm f/1.8 DC HSM Art Lens.  These are constant aperture zoom lenses and I prefer that over variable if possible.

[mikeficklonni]

I just want to thank everyone for their responses.  I really appreciate it. This is all very helpful information.