I think if they do involve the children in any commercial way, it would be (another) huge misstep. It goes against everything they've said or done so far regarding protecting their privacy and that won't escape comment.
Also, I honestly don't think the children are going to generate that much interest. I'm sure they are absolutely lovely, but there have only been tiny glimpses (which was a perfectly valid choice by M&H) unlike the Wales kids, where there is still limited exposure but we've seen them grow up so far and there is a bit of investment in them, as there was with William and Harry when little.
"Ta dah! We've changed out minds, here are our kids and we're using them to flog jam (or whatever)" would be a really bad look and appear cynical, because it would be cynical.
Happy to be wrong if they don't go down this path.