You can ask yourself two questions:

Is my child too sick to be comfortable at playschool and/or does my child have something contagious to other children or staff?

If you answer yes or are unsure, your child may need to be at home instead of class. Minor colds that can be managed by occasional need for tissues are pretty common in the winter season and we all just carry on. Persistent coughing and a running nose are likely to spread and infect others which we would rather not have happen. Children with a fever, even medicated from home, should not attend until well again.