GIMP is great for editing photos, but a poor choice for creating bitmap (non vector) graphics. It's a big hassle even just to draw a straight line in GIMP. MS Paint is the reverse - easy for graphics, ill-suited for photos.
As I noted elsewhere on this page, Kolourpaint4 is the Linux equivalent of MS Paint. There are others which aim for the same niche, one called (MTPaint? or similar?) for example, but I found them harder to use.