Although it's not that common, some children get SAD and it's perfectly safe for them to use a light. Remember that they are electrical devices so younger children should always be supervised. It's certainly not a problem to have the light on whilst there are children in the same room or if they come and sit with you when you're getting your light therapy.
There has been very little research involving babies and light therapy so, to be on the safe side, Lumie recommends you keep them from close exposure to a light.