Very nice work!
As a digital artist myself, I really enjoy it when other artists take an interest in the medium. I'm also a strong lover of painting cats!!! They're my favorite subject to paint! Our styles of painting are much different but I highly appreciate the multitude and variety of methods used in all art forms.
I really don't have a critique as much as it would be my own personal preference, but you should try and learn to not outline the features of the faces. Like the black outlining of the cats facial features, the boys and the girls eyes and face. But if this is what appeals to you, there's nothing really wrong with it, so don't listen to me! LOL!
I really like the boys hair. Nicely done. Although I'm not certain if you were painting in additional hair or trying to make shadowing.
With the exception of the outlining, the painting of the boys face is great!!
I'm not sure what the third painting from the top is, but it's fantastic!