How many classes should I work on the same topic, like Farms animals?
It seems that some of the children are bored after 3 weeks of the Farm animals subject, even thought I tried to have different activities in each lesson.


You have the right attitude, you are observing the class and thinking about how things can be better.

I’m not surprised they are bored after three weeks on the same topic !! Some teachers are perfectionists and do not move on until every single class member knows the target vocabulary perfectly. This may be thorough but it’s a bit too slow for the majority of the class. Students can become frustrated if presented for lesson after lesson with the same vocabulary. They have the impression that they are not advancing very fast and it’s true !

On the other hand the problem might not be the TOPIC but the way it is taught and the length of time spent on each activity. I can’t tell that without observing one of your lessons. But you will figure it out by continuing to notice how things are going and making adjustments. If students are becoming restless then change something – either the activity or the topic.

Here’s a way I really like to do lessons:
Introduce some new language in each lesson and continue working on previous topics as a constant revision process.

Start on Farm animals and do half the lesson on that. Then do a song and then some revision of previously taught themes – that way your lesson has variety not only in the things you are doing but in the topics. You can change the order around as you please but usually I start the lesson with the new things while the children are freshest.