My ten year old recently took up the clarinet in school. I played for about 6 years as a kid, up until end of high school.
She came home with the clarinet today, before having any lessons. I played some for her, and found the lower register real hard. I know I am out of shape, but given this is a rental instrument, could stiff pads, etc, make it difficult? It is a lot harder than I remember all those years ago.

possibly, but i tihnk it`s jsut that you haven`t played in a while... can you make out the upper register? if you can`t, than it just means that your lungs aren`t used to wroking like that, b/c they haven`t in a while... lol.. i played a new instrument, and i hadn`t played an instrument for an entire year, and when i played it, my ribs ached so much... b/c i wasn`t used to controlling all the air n stuff... if you play it a bit more, you should be able to regain all that skill you had in high school. but i`m not an expert at the clarinet, so i wouldn`t know exactly what would be wrong if the instrument was really broken

It could be the pads.

I play the clarinet too,a rental one and most of the pads were worn out , just slightly but it made all the difference because they didn`t cover the holes properly. I also had a problem with the lower register but when I got my own new one it played a lot better so it must be the pads.

it could also be how the lower joint keys are aligned. I know there is a major difference between my instrument and my student`s instruments in the lower register but that is because my lower joint keys are aligned so that they match my soft touch and theirs is aligned to match the hard touch they have right now.

I suggest taking it into a repair specialist and have them do a whole clarinet check, even the smallest leak in the top joint can cause the lower one to be hard to play.

a very good suggestion-ave it inspected by a professional, perferably one who likes to work on clarinets-the best way to locate one is to conatact the principal chari of your most local symphony orchestra- they usually have someone they know and trust well to do work on their clarinet(s)