Here’s what not to say if you want your child to trust you.
1. The ultimatum without follow-through

Kids know exactly how far they can push their parents, and are extremely aware when a parent has lost control and begins making impossible ultimatums.
Threatening to ground a child for life is kid-code for “never going to happen” and a sure sign that you can’t always be taken at your word.
Instead, to communicate a firm boundary, use a consequence you can actually enforce – ideally something that matters to your child that can actually be carried out.
For a teen, this might be taking away a smartphone or changing the password for wireless internet access.
Follow through with the consequence so it’s not an empty threat.
Children need to trust that their parent means what they say.
2. A threat of physical punishment

Rather than making threats of any kind in the first place – even if you have no intention of following through on them, it’s better to talk to children as people, and both listen to and consider their side of the story.
Mutual respect between parent and child go a long way toward maintaining trust.
“It’s important that parents are aware that it’s not only what they say but how they say things to their children or teens that can make or break trust,” says Jeffrey Bernstein, PhD, and author of 10 Days to a Less Defiant Child.
“Aggressive tone and body language can leave children and teens feeling less willing to confide in their parents.”
3. Invoking another authority figure

When parents sense that their position of authority in their child’s life is not being respected, it can often lead to their using other authority figures to strengthen their own faltering position.
Telling your child that you’re going to share personal information with their teacher is one way to break the sense of trust that your child has in you as a safe person.
Home needs to be a safe and private place for a child; it’s considered entirely separate from school.
Instead of making false threats of sharing personal things that should stay between the four walls of home, such as reluctance to help clean up or refusal to complete homework, try giving your child a choice between two things that you support.
For example, if your child is balking at homework, you might offer them the choice between working on it before or after dinner.
Giving a child a bit of power over their own time can yield positive benefits in compliance.