It's not even a good idea to let quite a lot of adults use ChatGPT. People don't know how it works, don't treat the answers with anything close to appropriate skepticism, and often ask about things they don't have the knowledge/skills to verify. And anything it tells you, you likely will need to verify.
It's quite unlikely to affect their personality, but it might make them believe a bunch of weird shit that some unknowable, undebuggable computer program hallucinated up. If you've done an uncommonly great job with their critical thinking skills, great. If not, better get started. That is not specific to "AI" though.