hi... getting an rp doesnt take too much time.. infact, if you apply with the right papers, you can get it within 10 days... here are simple steps to help u.

1) take all the required papers (relationship proof, bank statement etc etc) to the immigration office.
2) once ur application is accepted, they will put a temp visa on ur son's passport. this is valid for 3 months and he has to complete medical and fingerprinting within this time.
3) as soon as 2 is done, go for medical and x-ray.
4) view results online. once you see the results, you can then and there fill other required details (online itself) and take a print.
5) take print from 4 and go for fingerprinting.
6) once fingerprinting is done, go back to immigration. they will help you with the rest.