Hmm... I'm always hesitant to give Grand Canyon hiking advice to folks I don't know. I've seen fat people do OK and marathoners die so it's a crap shoot. If your a strong hiker and have carried your child before or can practice it before the trip, you should be alright. Just use your common sense and remember you are going downhill first so the self limiting factor of "climbing" is not there. As far as the weather, yes, it can snow in May. It is unlikely to pose a problem though. I've been there twice with snow in May:
http://www.expeditionportal.com/forum/showthread.php?t=14895
http://www.yotatech.com/f100/arizona-strip-grand-canyon-southern-utah-central-nevada-trip-212020/
...and both times it was a non issue. More of an interesting aside. The main hwy 67 from Jacob Lake to the GCNP is closed until May 15th so that gives you an idea. The powers that be are very conservative/cautious in that respect. As far as spots to go, it looks like you already have some really good threads and recommendations on tap. Where will you be travelling to/from?
Also, a nice site with lots of good trail info.
http://www.bobspixels.com/kaibab.org/bc/gc_trail.htm#north
I really appreciate the advice and concern. I think that the N. Kaibab trail to roaring springs is the only trail we will do that will go below the rim. For all the reasons you mentioned above I dont want to push it especially with the son and wife. From my research I'm pretty confident that I can make it to the springs and back with no problem.
If it was just my wife and me I wouldnt be concerned about cold/snow but I'm a little more hesitant with my son. Its harder to keep a baby warm and happy but I really would prefer my original dates due to my work schedule. I guess in reality I can wait untill its closer to make the call on when to go and watch some forecasts for the area.
I will be coming from St. Louis, so the plan was I-70 west then south on I-15. That will get me in the area I want to be in then jump over to Fredonia as a start. And from there I'm not sure the order of my destinations but I have started a google map and will update that and hopefully get it posted by the end of the week.
Again, I really appreciate the advice.