To provide a quick description of Chrome's Incognito Mode - it doesnt save any information about what you are browsing in terms of data. There will be no history or data to show whats being browsed. Comcast does not track anyones traffic to be able to tell you either. In terms of Parental Controls on the internet, please review this article: https://www.xfinity.com/hub/parental-controls/xfinity-parental-controls-on-the-internet
If you have your owned modem and/or router, you will want to refer to the manufacturer of that device for parental control options.
I've never used this, but it might be worth looking in to. It has a keylogger feature.