Little children are not wholly domesticated creatures at best, so the best thing about photographing them is that you never know what you will get! Only the older girl here is giving the camera operator what an adult could hope for – an entirely natural and engaging smile – all the rest of the expressions are out in left field: incomprehension, boredom, what the heck, what do you want me to do, are you done yet, do you know how to use that thing? Serves you right when you try to pose children. The dog couldn't care less but at least he has dignity. Best to get candid shots, a lot easier to do today than it was with a bellows camera with a 4 x 5 inch glass plate.
I knew a couple whose daughter exacted revenge: for about two years they could not get one decent photo of her because they once made the mistake of telling her to smile – from then on whenever she saw a camera she immediately froze and pasted on the most frightful version of a fake smile anyone could imagine in their worst dreams! My own sister was not told to smile and she rarely did for the camera when she was a toddler, but she always instantly squatted down and watched you intently. No one could understand this. Years later it occurred to me that adults squatted with the camera in order to get on her level – she was merely reciprocating!
Aren't kids great! They will make monkeys of you when they can.