I believe Sanji is pretty awkward around kids for obvious reasons (having an abusive father and an unconventional relationship with your real dad will do that to you) while Usopp is extremely good with kids because he has spent his whole childhood and teenage years taking care of the Usopp Pirates as an older brother of sorts. So when they're older and married and decide to actually have kids (post-Sanji having a breakdown about him being a good father) it's just so fucking funny to me.

Usopp, holding the baby: Do you want to hold her? Sanji: Yes. Usopp: You're- You're not- Pfft. You have to like, at least move to do this. Sanji: I want to. I won't. Usopp: You're going to spend all of your life without holding our kid, then? Sanji: I'm going to drop her and then I will have to kill myself for committing such atrocity. Usopp: Have I ever told you you're an idiot? Sanji: I am scared to drop her! It is a very rational fear! Usopp: You can carry at least forty plates full of food in both hands and legs somehow without breaking anything and you're afraid you will drop her. Sanji: Forty-five. And yes. Usopp: What if I let her fall like- Will you not catch her? Sanji: Just do not drop her???? Usopp: BUT WHAT IF IT HAPPENED Sanji: STOP TURNING THIS THING AROUND JUST GIVE HER TO ME I HATE YOU Usopp, giving Sanji the baby: Well, how does it feel? Sanji, holding back tears: She weights absolutely nothing 😭

6 y/o kid: Daddy! Do you know any cool games? Sanji: Hi, princess. Um. Don't you usually ask these things to, um, your other dad who also happens to be way better than me at these things? 6 y/o kid: But I want to play with you! Sanji, not having any memory of playing any games at all: .... Do you want to see a really cute rat I've been hiding from the crew? 6 y/o kid: YES YES YES Sanji: I'm so lucky you got that from me-

Usopp: Why are you in... The corner of the kitchen... Crying... Are you- Are you okay? Sanji: She called me dad- Usopp: It's been almost five years and I think it's time for you to stop doing this every day-

Sanji: She's so tiny Usopp: Yes, that's what happens when you're a baby Sanji: And she's clinging onto me and she won't let go Usopp: I am starting to think you often forget you're her father- Sanji, crying: I'm her fath- Usopp: Oh my god-