gb777,
If you as a
PR sponsor your male child for
PR, then he indeed does become liable to serve National Service (NS), as a second generation
PR. The easy way around this is to not sponsor your male child for
PR; instead apply for a long-term social visit pass, valid for 1 year, renewable as long as you maintain your
PR status.
If you intend to live in Singapore for the very long-term, your son can apply for a
PR on his own merits when he lands a job in Singapore. He will then be considered a first generation
PR, therefore not liable for NS.