Final answer:
To test a child's lifejacket, it should be tried on the child to ensure a proper fit, along with checking the straps and examining for wear or damage.
Step-by-step explanation:
A good way to test a child's lifejacket is to try it on a child and see if it fits properly. The steps to ensure a life jacket is safe for use should include checking the fit on the child it is intended for, making sure all the straps are secure, and examining the life jacket for any signs of wear or damage. While seeing if it floats is a basic check, ensuring a proper fit is crucial for safety.