Since its hardware they are interested in I’d really recommend getting started with an arduino. You can build a lot of cool stuff and there is a great community

Since its hardware they are interested in I’d really recommend getting started with an arduino. You can build a lot of cool stuff and there is a great community. For real in depth “computer engineering” an FPGA is the next step. But that requires a serious time commitment with a steep learning curve, and you won’t find nearly as much resources or hand holding.