Math difficulties

So me and my husband decided to start homeschooling next year. My kids want to finish out the year at their public school, which gives us plenty of time to figure out a way to home school. My son (almost 8) is in 2nd grade and doing wonderfully in reading and writing, but his math is severely behind. His teacher is concerned and even called me a few weeks ago about it. Today my husband was helping my son with his math homework and he was so disinterested and just unable to understand even the fundamentals.

Does anyone have any advice on how we can approach this? We’re even considering trying to find a way to bring his legos into the his math classes and even some online courses, but he just shuts those ideas down. He even refuses to write the numbers correctly because he believes it doesn’t matter. I struggled in math as well, but my son brings a level of stubbornness that overshadows mine at his age