Back when I had a job that required regular drug testing we WERE told to not eat poppy seeds. But my understanding is that, unless you have other digestive issues (not sure if a baby would count?), it is incredibly unlikely to test positive unless you are mainlining poppy seeds for weeks on end.
Your understanding is incorrect. It varies depending on the sensitivity of the test and the seeds being ingested, but it is actually quite possible for poppy seeds to trigger a false positive on a urine test for opiates, and it does happen. MythBusters tested this in their 3rd episode many years ago. They bought test kits that were publicly available for workplace testing and followed their instructions. They, like you, went in thinking it was just a myth. The plan was that they would continue ingesting foods with poppy seeds until they either got a positive test or they ate such ridiculous quantities that it wasn’t worth continuing. But they started getting positive results very quickly, (after just a few servings of either poppy seed bagels or poppy seed cake) and they stayed positive for a couple days. They called the companies that manufactured the tests and were assured repeatedly that it was not possible (because of course they would never admit that their tests can get false positive results). US Federal employers that test actually mandate that their tests have a much higher threshold because of this effect. But not everyone uses tests that adhere to that standard, and many are just way too sensitive.