Question

how we can reproduce a twin child

Answer 1

when  2 sperms fuses with ova, then we get a twins child
 it happens naturally

Answer 2

Giving birth to twin child is just luck. It happens when two sperms fertilise the ova at the same time. but it generally doesn't happen. When one sperm fertilises with the ova, a hard coating is formed around it. Other sperms can't penetrate the hard covering. So twins generally are not found. And you can't say whether twin child are going to be there or a single child.