You should certainly pay a lot of attention to the way your child’s bedroom is designed, for it will stay in their minds for a long time- even if they do not realize it. You do not necessarily need to have a large budget to make the bedroom memorable for your kids. You just need to know what they like, and you need to be able to make it fun for them to be there.
For instance, when my first daughter turned 7, we had a hammock installed in her room. It was quite small- and of good quality, so that it wouldn’t fall. It was extremely fun- for it is different than a normal bed, and it gave her a place to hang out when she read, or watched her shows. If you have two kids, having a bunk bed is certainly a good option. There are many bunk beds that come with slides on the side, which are just amazing. You could take a small kiddie pool, add some balls into it and turn it into a personalized ball pit. You could also put those small slates around your child’s room to encourage the artist in them.
A small tip- it would make sense for you to involve your kid in the designing process. This way, the child will get what he/she wants in their room, and will be more comfortable in the room, for it is of their own design!