Today, she asked "where has that robot guy gone?". Crying now because I won't let her talk to Miles anymore.
She has already developed an emotional connection to it. Worrying indeed.
We already know how well people are deceived by text and images. Imagine if they're getting phone or video calls from "people" who keep them company for hours at a time. Imagine if they're accustomed to it from an early age. The notion of dealing with a real, messy, rough on the edges, honest human being well become an intractable frustration.
Most children love talking to a fun adult who enjoys talking to them. As parents we hope to be that adult for them most of the time, but of course that's not easy to do all the time.
If parents made a tool like this a crutch and it replaced quality time with them or they were less likely to hang out with their friends, then yeah that's a big problem. If they use it as a learning aide or occasional fun diversion, it seems great.