Play a Few Games
Simply telling tots to smile just isn't going to work in most cases, so playing a few games with them can help. Tell them to get moving — to spin, roll, etc. When the giggles ensue, ask them to hug or kiss. If an older child is willing to cooperate but a younger one isn't — enlist the older one as your assistant and ask her to whisper something funny to her sister. Sometimes having another child act as the intermediary is all it takes to get the lil one to warm up to the camera.