Well, the teacher, is rounding up from the Thousandths place, meaning, they're looking at the 3, and, seeing if they can round the number in the hundredths place up. Since, it's a 3 in the thousandths place, the teacher keeps it the same, and, says 0.47 liters.
The parents are looking at the number in the hundredths place, and, seeing if they can round it up, since, it's a 5, and 5 or higher, you round up, they round it up to 0.5 liters.
I hope this helps!