There are clients to whom "guided posing" is a joke.
These clients are spontaneous, dynamic, highly expressive and volatile in their moment by moment emotions. They have the attention span of a hummingbird. Engaging with them while wearing an "I'm a serious photographer so let's get down to business" face is merely an act of desperation that leads nowhere.
Forty five seconds into what appears to be a cooperative session, they will glance into the lens of one's camera and suddenly take off laughing, at high speed toward some tiny object that has caught their attention - a dust bunny for example, which they will peer at and examine with all the scrutiny of a molecular scientist.
You'll walk up to them slowly, quietly; hoping to capture that intense, meaningful gaze with all the discretion of a floating pink elephant but in the six seconds it takes you to adjust your camera settings, the child has already crawled, with all the panache of a Navy Seal, under the coffee table at the far side of the room.
Your shock does elicit an apologetic but but slightly amused smile from the mother-slash-assistant, after which ensues a few tense minutes of negotiation ending in a some form of food bribe. When he's finally out in the open, you'll attempt a handful of photo opps in between mouthfuls of cheerios.
Once satiated, the child might allow you to coax him to sit still in a small chair for what amounts to 20 rapid fire images before he starts yelling boisterously - in a language only his mother partially understands - while stripping down to his diaper.
Photographing toddlers is like photographing birds, you've got to catch them in mid-flight or while they're perching. It's truly a "capturing the moments" deal between photographer and subject. Toddlers don't make it easy but the experience can be really fun. Except the occasional actor, there is no other "client" with whom spontaneity of expression and action are the foundations of a shoot. Since I don't have to worry about makeup or posing, the session is creatively freeing in some respect. My job boils down to pertinent observation, tricks of encouragements and knowing when (and how to best) click that shutter. And since toddlers look crazy cute under most circumstances - poshly dressed, bare bellied with diapers, naked except for cowboy boots, squatting over a seashell, covered in mud, you name it - the wardrobe options are near limitless!
So for parents who want to take better portraits of their one to four-year olds, make it easier on yourselves and hire a photographer. You could probably use a break from all that chasing around anyways.