As a minimum, check shoulder height of straps every 3 months, and adjust accordingly
One issue that is easily remedied by parents is to ensure that they position the shoulder straps at the correct height. This involves either rerouting the shoulder straps (please read your instruction manual for details) or with some car seats, simply raising the headrest which also moves the shoulder straps up. Once this is done, then buy the 5 point plus to eliminate the design flaw in the car seat harness to help prevent children wriggling out it!
It is extremely important to have the shoulder straps in the right position, otherwise the car seat will not give adequate protection in the event of a collision. This is a common problem as the child is growing all the time and often parents only use the car seat when they are just going somewhere and don’t have the time to check shoulder height settings.
Secondly, please make sure that you tighten the car seat harness firmly. A good idea is to: