Introducing new baby to a young toddler

Hi ladies,

I am currently 25 weeks pregnant with my second and I also have a 16 month old boy. And I’m wondering if any of you have tips on how I can start introducing to him that he will have a baby brother soon. Every time I try verbally tell him “mummy has a baby in her tummy “ or “you’re going to be a big brother soon” something along these lines he just looks like he has no clue what’s going on. And because of this pandemic he has never even seen a real baby 🤷🏻‍♀️ I really don’t want him to feel left out or jealous when baby gets here I want him to know “he’s going to have a baby brother” and not “mummy is going to have a baby” if that makes sense 😩