Pregnant again

Same. Explain to your first how it isn't their fault and how they were once that little and the constant attention isn't forever.

Some kids love being a part of the babies life and being a sibling and arent jealous at all.

You could also introduce a stuffed animal or blanket that is a comfort item to replace the attention you'll be able to provide

Start making minor changes while you’re pregnant so it’s not a stark contrast when the baby comes. Let your baby work on independent play and get good at it. My MIL suggested I get a baby doll for my oldest when I was pregnant so he could “practice”… he didn’t really understand or care but now that his sister is older, he plays baby a lot with the doll. I will also say, my oldest (almost 3 when my second came along) took a long time to warm up to her. I saw all the cute sibling videos and that was not my experience and I had to do a lot of grieving. Also, once baby comes along, spend 10 mins a day 100% focused on your oldest child (no baby, no phone, etc). I can always tell when I haven’t spent that dedicated time with my oldest because he starts acting out more.