If your kid really does need to be a blue bubble in the group chat (basically, if all their friends have iPhones and they say they want one too) then the most cost effective way is with the iPhone SE 2022.
The third-generation SE is the latest version, and is the only iPhone still sold with the classic design with the home button. It’s a very slim and small device with a small (and not great) LCD screen, but it has 5G and wireless charging (but no charger at all in the box) and access to iMessage, FaceTime, AirDrop, and all the other Apple-only things iPhones offer.
It might not be peer pressure, though – if as parents you also have iPhones, it can help to have your kids have one too as you can use the Find My app to keep track of their whereabouts.
There are pricier iPhones with more features and better cameras and screens, but for most kids the iPhone SE is more than enough. It will also get software support until about 2028.