If you're dead set on having the ability to bring your kid with you, I think the PA is about your only option. It's not really designed for it, but the boat is so buoyant I think you would be ok until hes a teenager. What kind of rack do you have on your Santa Fe? Anything rail based (I hate window/frame mounted) should be fine with proper rigging.
Also, the 12 is liftable, but its going to be a bear after a long day on the water or on a breezy day. Just make sure you are 100% confident in your lifting technique and practice before going out solo.
No joke, for anyone that is considering car topping their fishing kayaks, I STRONGLY encourage you to take an entry level olympic lifting class. If you can learn how to comfortably snatch and clean/jerk, you can car-top a moderately heavy (anything other than a PA14) kayak....
https://www.youtube.com/watch?v=9xQp2sldyts
https://www.youtube.com/watch?v=Cw0YyyJ8Tgw