No. Children learning a second language become confused if the people speaking with them mix the language, by using two languages in one sentence. The child can’t understand which words and rules go with which language. Our classes strive for 100% immersion so that no confusion takes place.
See this link for related research: Early Dual Language Learning

Research has shown that children who learn a second language actually do better in school—in language arts, creativity, cultural awareness, even standardized tests. Immersion programs have been around for decades and there has been a lot of research done on this question. (See links to research here.) Research consistently concludes that learning a second language does not put children behind in their first language (English) and there is a good body of research that shows a correlation between children who learn a second language and higher performance in other subjects. There are actually not many things in school that aren’t related to language processing, and learning a second language increases the child’s language processing abilities, which in turn improves their performance in school.

All of our teachers are fluent in the target language, love working with children and most of them have backgrounds in education or childcare.

Yes, we do background checks on all teachers before hiring them.

All teachers speak English (most of them fluently), but try not speak to the children in English except where the safety and security of the child requires it, or to clarify rules and expectations in a situation where a non-teaching staff member is not available to speak with the child. When a child speaks to a teacher in English, the teacher will facilitate helping the child use the target language as appropriate.