Mostly candid shots, though I do posed one too I much prefer the natural look.
Either can work, looking at the camera or not
I don't always use the 70-210mm f4, the Tamron 90mm f2.8 works very well for portraits too. With either lens you won't have any problems throwing the background out of focus even on a crop camera. The 50mm lenses, I have used those too for portraits. The advantage of using a somewhat longer lens other than compression, is it puts some more distance between you and the subject, and if you fill flash outside being a bit further away makes the effects of flash less obvious
I don't really have any strong feelings on zoom v prime, some do but I think it's really a case of right tool for the job and either will do a good job. For moving around subjects (kids at play) a zoom gives you more flexibility.