The best portraits of children are achieved when they're fresh and happy, feel relaxed, are comfortable and playful.  Having expectations too high can be unrealistic and add to the pressure the child may feel to perform.

Robyn is great with children and loves playing with them and will capture natural expressions, so there isn't a need to keep demanding smiles from them. 

Their eyes look so beautiful and huge when they are just looking into the camera.

Try to make the appointment in the morning when the children are happiest.  As the session finishes off, babies may need to be fed and are going to sleep.  This may also provide for some lovely images.