Help! Cats are peeing in the babys stuff!

Long story short my daughter got a kitten for xmas. At 6 months we had to put him down cause he had FIP. We decided to wait alittle while and just went back and adopted 2 kittens. Super sweet and cute all around both cats are awesome until now. They are about 5 months old now and we have started buying and getting things for our newest addition coming in April. I started nesting big time and noticed a smell in the babys room. Come to find out they have decided to pee on all her stuff! I've washed and washed everything 20 times until the smell was gone. How do I get them to stop? I guess I could keep the door closed the whole time but I feel like I shouldnt have to. Their box is cleaned daily and new litter is put in all the time. I cant get rid of them or my kids would be so upset. I just want them to stop. Thanks for listening ladies!!!