You can trap the parent Gigantoraptor (unlike what most tutorials say), but you must make sure it can escape. Create a stone trap using a gate that it can easily get in and out of. Lure the parent into the trap, shut the door, do minigame with baby, then open trap and run, and repeat. This is a strategy I just tested, and it worked perfectly. You have to make sure the parent can return to the nest, so make the trap close by, but still out of aggro range of the nest so you can build it. Regular stone gates work, no need for behemoth.