I need more speed Scottie

I was out at a family event, on a farm in Rochester with several families and more than a dozen kids. I decided to make myself the family photographer, as it gave me something to do. I was using my Nikor 55-200 f4-5.6 to get pictures of the kids. It was great during the day, but as the evening came, and the sun started going down I was getting frustrated.

In shadow, I could no longer shoot at ISO 200 with any sensible speed. I was down to a shutter speed of 50-60. Too slow to get kids. I bumped the ISO up to 400 then 800, but the shutter was still slower than I wanted. The lens is just too slow.

What are the options? Not much. The Nikor 70-200 VR f2.8 is huge, with a huge price tag of $1700. Yikes. Sigma has one with similar specs, no VR for about $800. Getting better. Even still, this wish item is likely to stay a wish.