It hurts, and unfortunately, they will probably paint you in a lousy light constantly, even though your relationship/arguments shouldn't even be a discussion they should be involved with as they are to young to understand and grasp the whole scope. Adult problems are adult problems.

The kids have nothing to do with your relationship with their mom. Sadly over time, they will take that as gospel and all you can do is hope they reach out on their own and ask questions when they get older when things don't start to add up from what their mom told them.

I wanted my nephews at my wedding but not my sibiling, and it's a package deal no matter what. Sadly it's a lose-lose situation for everyone involved and could have been avoided. You must accept that they are collateral damage from their mom wanting to wage war and put her feelings above them. I can't even send presents anymore (which probably helps vilify me), which hurts the kids for no reason other than spite.

But don't let them weaponize their children as leverage. It's a power play and a way to keep you/family in line and walking on eggshells instead of calling out/humbly checking their behavior for what it is.