You're getting divorced, and you have two kids. You also have attention deficit hyperactivity disorder (ADHD). Your spouse claims that they're going to use your ADHD as grounds to make sure that you do not get custody of the children. Is that possible?
Typically, it's just an empty threat. You could argue that ADHD is a disability and that you can't be discriminated against. That's a significant part of the Americans with Disabilities Act (ADA).
You could also argue that dealing with ADHD does not impact the children's best interests. That's supposed to be the goal of the custody situation. The only way you lose custody is if it's clear that giving you time with the kids would be detrimental to them in some significant fashion. Serious mental disorders can be used on those grounds, arguing that the home is unsafe for the kids, but that argument doesn't hold weight with ADHD.
Besides that, you can take ADHD medication. If you're using it properly, the disorder isn't a negative to the kids at all.
Finally, if the children have any disabilities of their own, you may be able to claim that you understand what they need and how to help them since you have a disorder and experience with similar challenges. This may actually make you a better parent than your ex.
As you can see, it is unlikely that ADHD alone will impact your child custody case, but the fact that your spouse has threatened to use it against you shows that the case could get contentious. Make sure you know all of your legal rights in case it does.