I just read that drinking coffee while pregnant can increase childhood leukemia. I drank it with both pregnancies! Dr said it was okay. What's the deal?

That's baloney. I'm sorry someone troubled you with something so foolish. Retrospective epidemiologic studies generate a huge amount of junk associations. Anyone who's scientifically literate can recognize the bogus ones. If I were to do a study to find out whether eating licorice causes your kids to be born with a unibrow, I'd get a positive result. Please don't worry about this.
As below. There is some inconclusive/inconsistent data re associations between mother’s caffeine exposure and ADHD, SIUDS cognitive development or, behavioral problems, leukemia. Given these limitations of available data, it is to avoid caffeine when Women trying to conceive or when pregnant or breastfeeding[try to limit caffeine .