I think a lot of the disagreement on this thread comes from knowing what a poster means according to your own situation.
See when I read the "buys and wraps presents for kids to take to parties" I'm not thinking of the actual task, which quite correctly, takes 5 mins online to order the gift, and then wrap in the paper we've already got. That's the bit with almost no thought required.
I'm thinking, I'm the one who thinks to check the kids bags for party invites, and respond. The one who knows another one of our DC has a dance lesson then, so is the party a "drop and leave" or am I expected to stay, in which case, need to make sure DH is free that day to do the dance lesson, or find out if DM can do it. The one who then finds out what the birthday boy is into, in order to buy something he'll like. The one who knows DD has grown out of the two party dresses she usually wears so I'll need to get another one by the weekend. The one who is thinking that DD will eat an early lunch at the party. But DS won't, so I'll do his lunch earlier, so then they will both be ready for an earlier tea. Oh, and buy and wrap the present.
None of this is difficult, or unachievable. But it's all the extra bit that is not just choosing to make extra work, but unavoidable. And a large amount is also non existent if I only had DD. Yes I'd still have to check for invites and get a new dress. But no juggling the logistics of where the second child is. No having to find out in advance if I need to stay or not because it affects the other child if I do. No alignment of when they eat so ones starving and the other isn't hungry. Incidentally, we have a 3rd DC. So logistically chuck that into the mix as well.
I know my mental load will reduce in part as the DC mature. With their increasing independency, there's less for me to think on their behalf. Right now, it's not something they are capable of, because of their age.
I think just because you can describe a physical task in two words, this doesn't really address the mental load surrounding it, for those the mental load affects the most.