@Linkat,
I am so sorry, Linkat. Us animal lovers know all too well how you're feeling right now, for having gone through the same sorrow, not only once but several times with our beloved pets. It's especially hard on children - I remember when our Max passed on, my daughter was just heartbroken and inconsolable for quite some time.
Luckily, you have another cat and a dog to band aid the pain a little bit.
It's never easy though.....