Leaving a child unattended in a vehicle with the keys in the ignition is never safe. Unattended children can accidentally cause the vehicle to roll or even drive away, especially if the engine is running.
Children can get bored during car trips and may play with the seat belt sometimes pulling the seat belt all the way out, locking the retractor, and accidentally wrapping it around their head and neck. Be sure to explain to them that seat belts are not toys. Any seat belts you don’t use should be buckled and locked to prevent getting caught, and make sure your child is properly secured.