Sorry to be negative, but I can't say I'm very happy with any of the suggested translations, or in fact with the proposed slogan itself. I know children everywhere are following the climate summit right now, and it's great to brainstorm on ways to raise awareness of the need for climate justice. I'm just not sure this particular slogan quite works.
The most glaring point is surely that it's simply not true. Very naive or very young children may not realize it, but everyone needs money to live, as well as a healthy planet. In the short and medium term, money is the most basic need of life for the majority of children, because families need money to buy food.
So the slogan as it stands could even seem insulting to the hundreds of millions of children who do indeed need money, especially those in third-world countries who have been forced to leave school during the pandemic and take up menial labor, precisely in order to live, to be able to eat. If I recall correctly, there have been estimates that the pandemic has brought back child poverty worldwide at levels as high as 20 years ago, wiping out decades of progress.
And of course saving the planet will take money, too. In the short term, it will take a lot of money, to pay for the transition away from fossil fuels and toward renewable energy, and to support the small countries most vulnerable to rising sea level and desertification. That's precisely what's being discussed at the climate summit, even though they're not making much progress.
Even if we set those big questions aside, there are still questions of grammar and word order in translation.
The indefinite article a / an doesn't work with 'earth,' because we don't have many earths, only one Earth, the earth.
'A world,' or better, 'a planet,' is possible, but still a bit strange, because the whole point of environmentalism is that we need this world, this planet. The children of the world can't expect to be saved by a spaceship and another habitable planet; this is the only world they will ever know. Children need the world, the planet, the one that is ours and theirs.
The singular pronoun 'I' also seems odd. Why not 'we'? Isn't solidarity the whole point, the need for a critical mass of people to come together?
So, if I had to keep something close to the original idea, I might go with 'We don't need money, we need the planet / our planet / our world.'
Or a little more loosely, maybe you could say 'I don't need a handout, I need a planet.' In that context, 'a planet' doesn't bother me as much, although it still reminds me of 'The Little Prince,' or sci-fi in general.
Either way, you would probably omit the comma and the period on the T-shirt, and visually separate the two contrasting statements, maybe putting the globe in between.