Last week I worked with three different schools in the Netherlands, all with different profiles. All of them are international schools, using a variety of national and international curricula. When non-English background parents put their children in these types of schools, they generally have very high expectations for the language learning opportunities for their children. Without getting into the benefits and pitfalls of English-medium instruction schools, a common expectation is that their children should acquire English and be able to use it 'like a native speaker'. A part of the expectation then, is that their child will have only 'native-speaker' teachers.
There are two issues with these expectations. The first is the presumption that education in English is a guarantee of a 'native speaker' accent and fluency, and the second is the presumption that native speakers are better teachers (of English, or in general) than non-native speakers.
Let's look at the first issue. Children who are in international schools are surrounded by people - children, teachers, parents - who speak many languages. In fact, odds are that they, like their parents, will interact far more with other non-native speakers of English than with native speakers (we are far out-numbered!). And even if they are surrounded by native speakers, where are they from? I hear frequently from parents that "a British accent would be preferable" - but what is a British accent? (And why would you say that to a Canadian??) The reality is that there is as much variation within native-speaker English as there is in non-native speaker English, especially in terms of accent. And even within, there is bias around certain varieties and how they measure up to the 'right' English. And beyond that, children who are in multilingual environments and are learning English at school may or may not develop a 'native speaker' accent, no matter what their teachers use. Accent development is variable for all language learners, even for children. While younger learners have a better chance of developing an accent that is not influenced by their first/other languages, there is no guarantee of this.
The second issue is one that puts a lot of pressure on schools, and can lead to poorer quality teaching rather than better. There is a common assumption that native speakers know a lot about their language, which makes them well placed to teach it. In the case of native English speakers, this is often not true. How we teach language/about language in the English-speaking world (to generalise) has not always been successful, and many English-speaking adults will be able to use the language very well but not explain why things are the way they are. Without a metalanguage and an understanding of how English works, we are often left struggling to explain our language to learners. I had to take several course in my teaching degree (ESL/EAL specialist degree) to learn about how English works, and how to teach it. Without that, I'd still not know my simple past from my present perfect. Teachers who have learned English the hard way often have better language knowledge, a better understanding of what is challenging in English, and are better placed to support language learners. If that teacher shares another language with some or all of the students, that is another benefit, and is useful in teaching contrastive awareness between languages. And even if they do develop something resembling a 'native speaker' accent, it is most likely to a less marked variety of 'international' English than an accent that resembles people from one area of the English-speaking world.
The bottom line is that we need to start thinking past who owns English, and what a desirable accent sounds like, and recognise that language proficiency is much more than accent. Likewise, teaching proficiency is much more than the language background of a teacher. The best teacher is the one that understands teaching and learning, speaks the language of the school with mastery (disregarding accent) and loves their job.