Eldest child talking like a baby

So, my 7 year old has recently (meaning for a couple of months now) been talking and acting like a baby. And it’s not just every now and then, it’s an every day thing. He whines and throws a fit over every little thing, which in turn causes my 2 year old to mimic the action, he talks like he’s a 3 year old again (saying dada instead of daddy, wa-wa instead of water, saying “give me puh-puh” instead of “can I have my puppy”) and he’s constantly barely sticking his tongue out when he talks to make that “baby lisp” noise. I have read all I can about it and how to stop it, because it’s honestly driving me insane. I’ve read that they do it a lot to get attention or when there’s about to be a big change, which is fitting because baby #3 is about to be here any day now. I also read that they do it to make sure they’re still loved and getting attention. But that’s the thing, his dad and I have never stopped giving him attention. We are constantly asking him to spend time with us, to color, play, go outside, build, dig, ride four wheelers, etc. I have done my very best to be patient with him, even encouraging him saying things like “you need to use your big boy voice around Bubby, because he’s learning how to talk a lot more now and if he hears you talking like a big boy, he’ll sound like a big boy too”. Honestly, nothing seems to be working, and with this quarantine in order, it’s becoming very difficult to listen to every day. Has anyone else gone through this? If so, what did you do that actually helped a lot?