First of all, don't worry about your kid's behavior. An experienced photographer knows how to get kids to cooperate. And they expect kids to be kids. Take a backseat during the session and tell the kids that the photographer is in charge. This way, you will be more relaxed, have fun and look great in the images as well.
I like to get the kids opinions during the portrait session, giving them a sense of "control". This makes them feel important, involved in the process, and leads to more cooperation. I never expect perfection though, and give them breaks to burn off steam between shots. We also get very silly.
Unless the photographer asks, don't talk to or call to the kids to smile while the photographer is taking their photo. Kids get confused and don't know where to look. When I need the parents to help get kids to look my way, or smile, I ask the parent to stand behind me so they will be looking in the right direction.
It's best not to tell kids to smile. This results in a fake expression. Instead, follow the instructions of the photographer if you are enlisted to help, it's better to get them to smile by acting silly, sharing private jokes, singing or whatever you do with them at home that elicits a genuine smile or laugh.
Two year old's can be a challenge. We kept this one still by putting leaves on top of the fence so that he could take them off again. That kept him busy just long enough to get this shot (and a few others) below.
The kid's in these images were two of the most energetic kid's I've ever worked with. So we did the poses quickly, gave them a lot of breaks. I would pose the parents first, then my assistant and I would bring the kids in and shoot very quickly.
When they viewed their images at the preview, mom and dad were surprised that we got any shots at all. Now they have these memories displayed in their home to enjoy every day. They also have something precious to pass down to the kids when they are older.
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