Question

Many children are diagnosed with mental illnesses. Which seem to be on the rise.

Is something missing or is it right

Answer 1

There should be a comma connecting the sentences. The second is a fragment (incomplete sentence by itself.

Answer 2

It should be:
Many children are diagnosed with mental illnesses, which seem to be on the rise.

Answer 3

Thank you

Answer 4

No problem! Happy to help!

Answer 5

Yeah, he's right :}