when you tap a lecture, make sure it is at L4, which can be located by following the iliac crests (supracrestal line, lumbar cistern). but in babies, that would not work because their spine / conus medullaris extends all the way to L4 so that would not be safe. also you have to make sure not to damage the caudus equinas when you tap, so inject the needle slowly and stay in the median plane so that the caudus equinas can move around in the CSF.