How can I develop language in a bilingual household?
If you have the chance to raise your child bilingually, do. It's such a gift to be able to access another language and another culture.
Generally, we advise parents to talk to their child in the language they're most competent in: their social language. So if Bengali is your home language, then use that language with your children because that's the language that will help to build their relationship with their family. This, in turn, will give them a solid foundation upon which an additional language, such as English, can be learnt.
It is increasingly common for one parent to speak one language and another parent to speak another language but then there might be a third language, a common language such as English where they will use that to interact with each other.
Use the language consistently; it's the consistency that's the key here. Try to let your child have times when they can play with other children who do speak your language.
When another language is introduced, your child may go through something called a silent period where they might not talk very much. But that's absolutely fine and nothing to worry about.
The benefits to their language, learning, and social development will be huge.