I don't think you need to live together for you to meet his children.
If he feels the time is right, why not go for it?
It might be easier for them to meet you somewhere else, where they don't have to be around you constantly (like a park, a fair, a pool, etc.)
It might be a bit awkward for them to meet you for the first time.
However, if you absolutely do not feel ready for it, don't let yourself be pushed, either.



