You were told correctly - The 5D is better suited for landscape , the 7D for wildlife because of the speed (due to smaller mirror - also less vibration and noise ) and crop factor of the telephoto lenses !
One other thing to consider is - you will get greater depth of field with the 100mm - if that is field relevant for you ?
The DX lenses are smaller/lighter for the equivilent magnification, and the frame rates are higher with less vibration because of the smaller mirror.
Even though you and I both are Canon shooters, I think you should look at the Nikon 135 F2 DC lens ($1400 )! You can use the Nikon lens on your Canon with a focus confirm adapter. Go to kenrockwell.com for a full review of this extraordinary lens !
I DID read the above - and that is why he did what he did !
The laws of optics is WHY 50mm was chosen for the 24X36 format. In 1926 optics dictated that the BEST lens would be slightly longer than the diagonal of the format - approximately 50 degrees angle as it turns out. These laws of optics are still true today as the best lenses are 50mm !
When I need higher resolution, I just load Velvia into my film cameras - preferably Pentax 645 - and scan to 36MP or higher !
Consider yourself lucky indeed as you apparently got a good one - IF it continues to AF properly !
Well, I have been having thoughts of the 5D II also - but I would use it only for lanscape work because the crop sensor is better for wildlife. BUT, if you shoot Velvia in a film camera and have it scanned, the results are equal to or better than the 5D! I decided I could buy a lot of film and processing for $2000 - the price of a used one. I already have an EOS film camera anyway. So, that is where I am at.
WOW, I guess I misspoke - I was looking at a dated B&H catalog - the Canon 250D in 52mm is $120 now at Amazon ! and lets you focus to 9+ inches.
Just for fun I looked at the Photozone resolution figures for the 50 1.4 - and they are 2598 center, 2382 edge at F4 which is the peak. For the 24-105 at 40mm and f5.6 the numbers are : 2406 / 2241 . All these numbers were done on a 5D II sensor. So, the 50 IS better and it is enough that it can be seen in your images !
Sorry, I misunderstood - I thought you were doing All the kids at once - but even at 12 at a time it would be nice to have high resolution.
The 50mm is the sharpest lens of any manufacturer - PERIOD. See kenrockwell.com for explanations.
Well, if you are not tired of reading yet, I would get a Canon EOS FILM body to shoot this with. Next, I would buy, rent or borrow an excellent lens ( full frame ) that had 28mm - preferably a Canon 28 f2.8. You will need all the resolution you can get !
Well, if you are not tired of reading yet, Here is what I will say - The simplist and cheapest macro is a 50mm F1.8 standard lens with a special 2-element close-up filter - Nikon made them in 52mm screw in size and Canon still does make them - the 250D - $75. The 50mm f1.8 will cost about $120 - AND the quality is is very good - you will be astonished how good !