Hide them under the bed so your mum doesn't see them. Lol
I think you have to remember that doesn't matter what animal you choose at some point you while need a vet. At the height of animal keeping I had about 21 hamsters & each vet bill was £25 each.
I've been told that rats are very clever & amusing but you need a massive cage, The ones are 3 by 3ft but they could need more. They live between 2 to 3 yrs.
Sorry I don't have a clue about mice, gerbils are so fast I don't think you would be able to handle them.
Hamsters are the best, but I'm biased they live 2 to 3 years. You would be cruel if you put them in any less than 120cms long x 60cms deep.
Mine live on sawdust lots of shredded toliet paper for bedding. (Don't be tempted to use anything else)
This could be a longggggg post so if you'd like to know about just let me no.