I have a D5 and S2 so I did order WAW flowers for Mom Day. Signed it from them. I am totally not looking for ANYTHING in return. If see says anything(Doubtful) I will just say the kids wanted to do that for you.
She is still their mother, I can never change that.
Depends on whether there is any kind of A going on. If not, and you're trying to rebuild the M, then sure, but if there is, then she has abandoned you and your M in the most fundamental way. If she wants to get something from the kids for Mother's Day, let her arrange it. Just because you are the kids' father doesn't obligate you to handle it.
Age of the kids is beside the point, my kids are little too. You are now only responsible for your relationship with the kids, not hers.