I have three kiddos, my oldest is 4 going on 5 and has asked many times to have her own playhouse on the place..and since the Little
House on the Prairie are her favorite on the shelf she will only settle for a log cabin. Took her out yesterday for her first few hours of cutting wood and spent most of it looking at wild flowers and deer. A few questions for those of you with extensive cabin experience- I am doing butt and pass corners, do you prefer the long 12-14" screws or traditional spikes to connect the logs? It will only be 8'x8' with a little porch off the front so not too big of spans to deal with. Also should I put it up on a treated post foundation or right on the ground as I really only expect it to be played in for the next 5-7 years.

When she out-grows the cabin, if built correctly, you may find other uses for it, so I would build it right. Depending on log size, you could stack the first row on treated 4"x material. I would simply use galvanized spikes throughout, pining the first course to the 4x material, and end-spiking the log end together. Pre-drill for the spike, of course using a slightly smaller bit than the spike. Structural screws are very expensive, also.

AK vikings advice about building on PT base is spot on, additionaly, debark the logs if you want longevity.
I know everyone want to see logs on the interior, but if you observe Scandinavian and Russian log construction (the experts and originators of log construction), you will see that most of their interior walls are furred out, often with insulation between the logs and the interior surface. This is something to consider.