The Canon 85mm EF is a SOLID performer. A lifetime lens in my book. The 70-300 f/4~5.6 I am not familiar with at all. I read this very proficient Canon reviewer's review about the "new" 70-300 Canon has...honestly, NOT very impressive a lens for that kind of money, and the lens loses maximum aperture fairly fast as it zooms longer...as he says, the 70-200mm f/4 L IS USM lens "
becomes faster than the 70-300 at 85mm"--which is a nice, subtle way of saying the 70-300mm dips to a slower max aperture than f/4 at the 85mm length...and of course, at 200mm, the 70-200 is still an f/4 lens, whereas the 70-300 is STILL an f/5.6 lens...ehhhhhhh.....
The 70-300 is a SLOW zoom, and it uses Canon;s second-grade focusing motor system...I would not really want it for soccer, myself. It just sounds "meh" from tis guy's review, and there's also the absolute necessity to make 100% SURE which 70-300 USM lens you are being sold; there is an OLD version of this lens. The newer model does not sound particularly well-made, and honestly, I thing the cheaper third-party offerings like the Tamron 70-300 might be as good.
Read the review; the Canon 70-300 sounds, honestly, unimpressive as hell...I sure would not want it as my sports lens...I think it would money badly appropriated at $659.
Canon EF 70-300mm f 4-5.6 IS USM Lens Review
As he mentions the Canon 70-200mm f/4 L IS USM is sharper, focuses faster, is a better lens.
I think, honestly, I would look for a clean, used 70-200mm f/2.8 L IS USM Canon....meaning the NON-IS, first-generation f/2.8 USM model, and skipping the 85mm entirely...maybe $950-$1100 used? Not sure at current market prices, but you do not really "need" IS for sports.
My feeling is that, moving forward, with higher MP cameras, that the Canon 70-200mm f/4 L IS USM, with its professional-grade optics, constant f/stop of f/4, and solid build is one of the three best places to drop the money, and CROP in later, using a professional-level optic. He compares it against the 70-300...the f/4 zoom is an L-series, with better optics. He says his personal preference, as a full-time lens reviewer, is the 70-200 f/4 L IS USM, and I would agree with his conclusions.
Welcome to serious photography. There are very few "cheaop" lenses that are any good at all, and for sports, a "Cheap" lens is the 85/1.8. Once the focal lengths get longer, the prices go up. The 70-200/2.8 zoom is the "standard" utility lens. Canon's 200/2.8 prime is affordable, but has no zoom, but is sharper than a zoom. A really GOOD lens can make very sharp images that can be cropped a good deal. While modern zooms are pretty good, prime telephotos are sharper.
Soccer is a sport where as the kids get older, the fields get bigger. And the players get faster. I would rather have the older, Canon 200mm f/2.8 "prime pipe" than the 70-300 4~5.6. I own a couple slow 70-300 lenses...they're not really that good for sports and action. They are "okay", but there are better choices that cost more, but which really are better. $659 is way too much money for a half-way lens.
200mm f/2.8 prime: best bang-for-dollar, light weight, easy to handle, good price
70-200 f/2.8 L USM (generation 1, used, no IS, but VERY sharp; buy a clean low-use one)
70-200 f/4 L IS USM: professional optics, designed for the higher-MP cameras of the future