What should i write in response to family visitor visa refusal?

I am a student in the UK and recently my wife and kids applied for a visitors visa. My wife was given but the kids denied on claims that not enough evidence was provided to show that she was the mother,however the birth certificate provided. We are planning for a reapplication with other doents like family pictures but i want to know, what should i write in response to the initial refusal as i really want to see my kids?