Can a child have liquid albuterol and a breathing treatment at same time, or do you wait for some time in between them?

Wait. Liquid albuterol is a very ineffective treatment for wheezing. And, as far as I am concerned, should never be used. However, you definitely do not want to give them at the same time. Throw the liquid away!
I wouldn't. I haven't prescribed liquid albuterol in more than a decade. To achieve the equivalent effect of a well done inhalation treatment with liquid albuterol would have too many side effects to continue. I wouldn't use it at all.