Their little mouths are just so small. It's about the same diameter as the 1ml syringes, maybe a little bigger but not much. Longer than syringes too, about 6 or 8 inches long, baby asprin would probably fit perfectlyI don’t have small hands and that antibiotic my Runner was taking was pretty good size. I use the needless 1 ml syringes to give liquid meds. Is this one about that size? Only problem I’ve had so far was giving baby aspirin they are so tiny it’s Nerve wracking making sure my hand holds onto the pill long enough to get it in the right hole. So that might work great for those tiny baby aspirin.