Why though?
Kids tend to revert to using baby voices or acting like babies when they're:
1. Embarrassed
2. Seeking nurturing
It's nothing to worry about. It's a behaviour, it's communication and it's a cry for help.
It's not something you need to try and stop them from doing and it's causing no harm. They're just letting you know they need some more nurturing, some more connection, some babying. And it's ok to baby our children, they're only this young once.
If your child is using a baby voice, take that as your cue to help them. You can make it playful and treat them like a baby: "Oh my baby, come here, let's have a big cuddle, what a cute baby, you can't even talk yet!" Then just connect with them normally.
Notice patterns of baby talk. When does it happen? What are you doing at the time? By making note of this you can predict times that your little one is going to need more connection from you and you can provide it before they ask for it.
You've got this.
Watch the full reel here