The content area that I first took interest in designing a CLIL lesson is math. Going through our first grade English textbooks, I found 70% of the content that could be easily incorporated with the Math lesson in the first grade. The English language used in the math lesson is not inaccessible for the learners, and activities involves manipulatives that induce speaking.
In a lesson that operates with two languages it can be friendly, accessible, and not too terrifying for the children.
Life curriculum is also a great entry to a CLIL lesson. Personally, I think it is easier to start in the second grade not the first grade because the learners (at least with the amount of language exposure in my school) are better equipped with language skills to understand the content and to comfortably respond in class.
First grade life lessons requires the learners to learn about group life, respect others and spend most of their class time sharing opinions in the mother tongue they are still developing. With limited amount of instructional time (in my school), I would choose to postpone their CLIL lesson to the second grade.
Our school has a strong P.E. team and a school-based curriculum, developing the learners athletic skills according to our own needs and strengths. Yet sadly, we have only one period of P.E. lesson taught by the P.E. teacher. I was lucky to be able to work as a first grade P.E. teacher for an entire school year, great experience and led by a wonderful coach in our school. The bilingual P.E. lesson was only administered for two semesters, not enough to come to any conclusions. Yet, the students were up to the school P.E. standards. I was teaching P.E., not English.