Whether you're taking a child's portrait or a group portrait, set your camera in its fastest drive setting. You don't need to machine gun the shutter release, but shooting in short bursts will ensure you capture a fleeting range of expressions.
It also improves your chances of getting a shot where everyone's eyes are open in a group portrait.
Even if you don't capture everyone's eyes open or their beaming smiles, having a range of shots taken fractions of a second apart means you can easily swap faces in Photoshop.
