I don’t think you can - ie the little one won’t get their own seat until they are two. Hence Club might give more space in total.

We flew economy domestic many times before my daughter was two, and typically got three seats near the back when checking in.

We used to get early afternoon flights, and without fail she’d sleep for the most part.

She’s four now, and about to go TATL for the first time. In club, so I’m setting her expectations too high at such a young age.