Simply replace the unfilled areas such as "" and "[date]" with your information.
It is that time again that happens once a year, where you turn one year older. As [I've/We've] watched you grow older year after year, [I am/We are] constantly overwhelmed by what an amazing person you have become.
[I/We] want to wish you nothing but the best on this, your birthday. May you have many more wonderful years ahead of you my [son/daughter]