Mounties say the overnight crash involving a sport utility vehicle and a loaded semi-trailer tanker happened on Highway 39 just west of Warburg.
RCMP Sgt. Gary Hollender says the tanker caught fire after what investigators believe was a head-on collision.
Hollender says the woman and baby were killed instantly, but the truck driver wasn't hurt.
The names of the victims have not been released and charges are not being considered.
Highway 39 was closed for several hours following the crash.
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