This OP posted this question 4 months ago. I would bet his wife and child are back in Canada by now.
When you apply inland and choose to travel outside of Canada, you have to remember that we are NOT all treated equally when it comes to the ability to re-enter Canada. The box on the page uccemebug noted specifically points out where the more serious difficulties lie. Foreign nationals from visa exempt countries or those with a valid visitor's visa will have an easier time re-entering Canada even though they have an inland application in process. At the POE, showing proof that the inland application is in process will help a great deal. Plus this woman has a Canadian child with her. Now, if the woman was NOT visa exempt and did NOT have a valid TRV, her chances of getting a new TRV to be allowed re-entry are next to nil, UNLESS, as angelbrat pointed out, there was a specific and urgent reason for her travel. Even in that case, it would be recommended that they apply for a new TRV before leaving Canada so they would know if they could re-enter.
Not travelling while an inland application is in process is a RECOMMENDATION, not a RULE. It can and has been done lots of times but there are risks and a person should be well prepared at the POE as well as knowing what the consequences may be. There are reasons people choose to take the Inland route when applying for PR to Canada and specific policy associated with it. However, there are lots of people whom, IMHO, wrongly choose the inland route when outland would have been a better choice for them. That being said, each application and process that goes with it is assessed INDIVIDUALLY and there is no "catch-all" that fits everybody. Be careful with that. I know the government tries to say that this stuff is easy but there is a LOT of consideration that has to go into every stage to be truly well informed and then weighed against each person's own personal circumstances. What fits them may not fit you.
