It doesn't really work the same way "-mainen" does, it's similar, but results in a word that has a more definite meaning.
"Lapsimainen" would mean childlike or childish, while "lapsukainen" only ever refers to an actual child in an endeared way (or if used to describe an adult, would be like saying "my sweet summer child" in english).
The Finnish suffix "-kainen" is used to create nouns that refer to things or beings associated with a particular quality or characteristic. Even though we don't necessarily mentally associate it with a similar meaning as "-mainen", it still is. Hence the translation of "bearlike" is close enough.
Close enough, but not closest. I would say "Bearie" is closer. You wouldn't call an actual bear "bearlike" but you might name it "Bearie".
I didn't say "mainen" and "kainen" are dissimilar, but they ARE different. By about the same amount as the difference between doglike/doggy and doggie.