He thoroughly bungled fatherhood back in Season 4 when he first lied about having a kid and then pretty much set the kid up to be kidnapped by Damien Darhk, so there’s really nowhere to go but up for Oliver from now on when it comes to fatherhood.
Stephen Amell seems pretty sure that actually acting like a father will force Oliver to be more responsible than he has been since we first saw him back in the pilot.
The Season 5 finale actually got Oliver over some of his lingering father issues as he faced what his dad did back when the Queen’s Gambit first went down, meaning that he he may be in a more emotionally stable place for fatherhood in Season 6.