Evil Thoughts While Nannying

When my six year old charge (btw, I am young and have no kids of my own) tells me he NEEDS random stuff like to keep playing or to take a giant, dirty rock home, or that he CAN'T do something incredibly simple like take his backpack with him when he goes upstairs, I routinely say:

"No, you don't need that."

"Yes, you can. You just don't want to, so don't tell me you can't."

I just can't even pretend to humor a child saying he NEEDS something totally random like to play with his toy for five more minutes, and I feel no sympathy when he has a sobbing meltdown over something stupid* like me telling him we have to go to school now and I am sending him in with his water bottle instead of giving it to his baby brother to drink out of (his baby brother has his own bottle, so I don't even understand this one). And I just get frustrated when I ask him to get a pair of socks to wear for the day and he gives me a wailing "but I CAN'T!" when there's literally no obstacle to prevent him. When he's genuinely in need I'm there for him, but the tantrums over stupid shit? NOPE.

My response to the bottle incident this morning:

"He has his own bottle, I'm sending you to school with this." *the tears begin* "You don't need to have a meltdown over every little thing, Child'sName. Come on, get your shoes."

Should I not be dismissing his concerns as totally invalid? Because sometimes they kind of are, but it probably feels shitty for him to have me act that way. But twice I've basically told him the meltdown he was having was immature, and both times he calmed down instantly. I feel like the only response to a child telling you they CAN'T do something totally easy (that you need them to do in order to get them to school on time) is to deny it, because what else can I say? I also feel like he only uses these words because he's learned that "can't" and "need" are more powerful than "don't want" and "want"—but he's abusing them shamelessly and I'm not going to humor it. Today I prompted him to drink up his juice because we'd been playing outside in the heat, and when he said he couldn't and I asked him why he couldn't, he finally responded, "I don't wanna right now." And I was like, "Okay, so say you don't want to, don't tell me you can't! Don't tell me you can't do things when you can do them!" I did not make him drink the juice, because I am not the Juice Police and it's not a big deal whether or not he drinks it. If he's thirsty, he'll drink.


Anyway, this has been a childcare vent. Similar stories? Advice?

*I'm pretty positive I've never even used the word "stupid" in his presence, so don't worry—I'm just thinking it's stupid, not telling him so.