According to the CIC website: http://www.cic.gc.ca/english/information/pr-card/arriving.asp
Permanent Resident Card: Arriving
If you are immigrating to Canada, you will receive your Permanent Resident Card by mail.
If you did not provide a mailing address when you were granted permanent resident status at either a port of entry or a local Citizenship and Immigration (CIC) office within Canada, please contact the Call Centre as soon as possible (see Contact Us at the top of this page).
You have 180 days to provide this address.
If you do not provide a mailing address within the 180 days, you will not receive the Permanent Resident Card. You will then need to send CIC an application for a Permanent Resident Card and pay a fee of C$50.
He will not lose his permanant residency status if he doesn't get his permanant resident card within 180 days, he will need to apply for a PR card once he returns to Canada.
He can apply for a travel document to return to Canada. http://www.cic.gc.ca/english/information/applications/guides/5529E.asp
Full details of PR card issuance are available in ENF27: http://www.cic.gc.ca/english//resources/manuals/enf/enf27-eng.pdf
10.1. New permanent residents
Since June 28, 2002, persons who become permanent residents receive a PR card
within weeks of receiving this status. New immigrants selected under IRPA are
automatically processed for a PR card as part of their application for permanent
residence, as long as they provide an address and all the information required for
producing and delivering their card. Once the Card Production Facility produces their
card, it is sent directly to their address by regular mail. Unless these persons require
photo retakes, or their presence is required to clarify vital information on their
Confirmation of Permanent Residence [IMM 5292B] or in FOSS, new permanent
residents will not normally be seen by local CICs.
New permanent residents may approach CICs regarding their status if they are required
to travel immediately after arrival without a PR card. Persons in this situation may be
unable to finalize the processing of their PR cards within the 180-day limit as prescribed
in R58(1) and should be counselled at ports of entry and/or inland CICs of the provisions
of R58(2), including the additional cost and detailed documentation requirements of a
new application for a card. If the person still intends to sojourn abroad prior to receiving a
PR card, an application for a travel document must be made at a visa office in
accordance with OP 10, section 17.
If you flew to Canada to submit photo's, you would need an address in Canada to have the PR card sent to... they will not mail them overseas.
As you have already landed (and thus are PR's) I would write to CIC explaining that you intend to return to Canada in 12 months, that you will apply for a travel permit for your son and once in Canada will put in an application for a PR card for him.
