Summarize this article:

If you see that food has been spilt on a toy or that it got dirt on it when your child was outside, take the initiative. Any sign of dirt or grime is an indication that the toy could be carrying disease. Your childand by extension youwill never be well if they go back to playing with the same toys that they were using when they came down with a cold. Anytime your child seems to be showing a case of the sniffles or diarrhea, assume the worst and start sanitizing everything they have come in contact with. If other kids have come over to play, they have likely touched the toys. In the process, they could have spread illnesses from their house. Clean up immediately after a play date. Even if nothing in particular has prompted you to clean your baby's toys, you need to clean at regular intervals. Planning for a monthly cleaning is a good rule of thumb. It can be easy to forget about big toys, like dollhouses, but these need regular cleanings too. Clean the surface and insides of larger toys. Clean the surface of the toys with your chosen disinfectant. Then, wipe away the solution and allow the larger toys to air dry.

Summary:
Clean when you notice dirt or grime. Clean after your baby has been sick. Clean after your baby has visitors. Clean at least once a month. Remember the big items.