According to the Eyfs, babies and children under 3 should never be exposed to traditional 'themed' activities - they are too young and our remit is to follow their interests.
In fact, there is a school of thought which says that themes are not appropriate for any children and all planning should be done from observations of what you have seen and heard them doing and saying.
Generally accepted good practice says that after the age of 3, when they are starting to need some firmer structure to their days beyond their routines, children might be introduced to subjects which will interest them such as looking at minibeasts etc.
Up until then it is play that follows their schemas, learning styles and interests.
Hth