If you have the experience and your son is a good paddler, it's hard to pass up the opportunity to paddle the Manigotagan from Caribou Landing to PR 304.
Bird River from Tulabi is a good route. Depending on your skill level it takes roughly 3.5 to 5 hours to reach Elbow Lake where there is camping.
I did a two night trip there last fall. Day 1 we left Tulabi around 11:00am and finished around 6:30pm at the end of McGregor Lake. There's a really nice spot for one tent at the beginning of the portage to Snowshoe. We single tripped our portages but didn't paddle too hard and stopped for a beer break and a lunch break.
Day two we fished and slowly made our way back to Elbow Lake. Day three we had an easy paddle back to Tulabi.
The new interactive Nopiming map is nice:
http://www.gov.mb.ca/conservation/nopim ... index.html