At the end of the film, after Beech and Tech 49 Jack sacrifice themselves and destroy the ship Julia is then seen with a child (who looks about 3 years old). She is then re-introduced to Tech 52 Jack and the way I perceived this was Tech 49 Jacks child but how is this possible if he is dead and there was nothing more than a kiss shown to happen between them?
The "Jack" who found Julia and saved her from her ship wreckage, slept with her at the hideaway, this is when she got pregnant. A year or two later, the other "Jack" was found and brought to her. All of the "Jacks", had the same memory of Julia...thus, they still loved each other.
Julia was in Delta sleep for 60 years. She might have been pregnant before Delta sleep. Delta sleep apparently halts aging and embryonic growth, until the person wakes up again.