Nia whom Robbie (Kyle Ward) met while on the lam purposely hid his child somewhere in the field where they were hiding, forcing him to have sex with her.
We see six very short flashback scenes of David and Gail making love (from few frames to 2 sec) that clearly show what is happening but we see only their faces, or back, in one scene we see Gail sitting in David lap facing him, but he's wearing trousers.