It is very important that your child gets a good education – in his first language and in his second language. If you talk to your child at home in your first language, continue to do so. It is very important that you can communicate with your child well. Use the language that you feel most comfortable with – if you try to talk to your child in a language you don't speak very well yourself then he won't learn to communicate very well either!
If your child has difficulties in learning both their first language and English, then it may be that they have more of a speech, language or communication need. Because English is an additional language, it is sometimes hard for teachers to recognise these difficulties. If you are concerned, get help and advice at local services.
To help your child, find a community group for your child to join. These groups may be in his first language or English, but may be useful in supporting communication and social development as well as perhaps his school work.
If your child would benefit from some additional support in the local community or at school, find them a mentor. A mentor is a trusted adult that speaks his first language and who can help him with learning English and that can be another shoulder to lean on. There are organisations that can help to find a mentor. Ask the school or local community organisations.