My daughters are three and a half and two years old. Of course they know me well and don't get excited when they see a camera, but my advice is to let the children feel comfortable. They will relax when they notice that you are relaxing. If you get nervous with your gear they most probably will try to avoid your radius. And if you feel inspired shooting them they will go with the flow. But beware: they are very quick, so choose a set which will give you the chance to react fast.
Getting closer with wide angle lenses is great, if you are shooting with manual focus taking pictures the with hyper focal will help you. I like 35mm (see below), 85, 50, 20 and 24mm (in that order) for instance. If a costumer prefers the "Contax645 Zeiss 100/2 with the lens wide open and Fujifilm 400H overexposed" look, it's a little harder than with, say, a Nikon with AF.
I like to shoot my daughters with a Pentax ME super, Nikon F4 and a 500 C/M (because I like to practice). With the 500 C/M, I like to come closer with the 80 Planar and the 50 Distagon. On the F4, a DW-20 waist level finder is nice - and the waist level finder of the Hasselblad is nice as well, because you don't get too much attention when looking down.
With a DSLR, everything should be fine, but avoid noisy programs like loud sequences of 6pics/sec and such.
And if you see their backs too often, try to reduce your attempts to get their attention to a minimum. Say their names nice, soft and friendly, they will turn around for a second.
Maybe you have a reward after the shooting? If you have a pola-back: go for it.
Saturday: Les sœurs by
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