Car seat straps should be snug when you place your baby in the device. They shouldn’t be so tight that they leave a mark, but it is important not to strap them too loosely either. The shoulder belt needs to cross at or slightly below your child’s shoulders and the lap belt requires placement low on their hips or pelvis.
The AAP recommends checking car seat fit regularly with this simple test: grab both of your infant’s arms and pull up while he/she is still buckled in the harness system. Your child cannot lift his head more than an inch off of his car seat if everything fits correctly – especially when compared to how much room there is between him and the top of carrier (usually more than an inch). If the harness doesn’t fit snugly, you need to adjust it.
The straps should be tight enough to keep the child from slipping out of the seat; If a child is wearing bulky clothing, the straps may need to be loosened; Never loosen or tighten a strap while your child is in their car seat because it could cause injury; The top tether strap should always be secured tightly at all times; To test if you have tightened the straps correctly, try picking up your car seat by holding onto just one side of the handle and see how much it moves.