There are 4 Islamic studies textbooks for grade 1 to 4 available at Free Islamic Textbooks. I haven’t downloaded all, so I can not review all of them personally, but the one I downloaded seemed good though not much interesting. But they can be used as spines if you want an Islamic curriculum. You can add activities here and there to make them more interesting insha Allaah. Unfortunately the textbooks contain drawings of animated beings, so make sure your child knows it is wrong.