This is great! I have been playing a child alone, pushing the game to its max, and finding the best carefully updated apps that add more child abilities. I am always looking for imaginative challenges that can be adapted for a child alone. One of the hardest things about playing a child alone is that they cannot move to a new lot without an adult. I think they can switch from one household with an adult to another household with an adult. I think I could adapt the nanny assignment to a pet-sitting assignment.
I also found the Globetrotter challenge interesting that requires the sim to stay entirely in Komorebi, which is really hard for a homeless, and extra hard for a child-alone that cannot harvest plants until level 6 mental skill. Your challenge would provide a home for the sim in Komorebi, which is completely different than trying to survive on the public lots. And your order of assignments works for a child with the gardening assignment coming second instead of first.
I know some people have very narrow and sweet requirements for child sims, but having grown up with only one American parent, I have experienced childhood outside the USA and I play some of my child sims with independent personalities and responsible roles. This challenge is obviously not entirely appropriate or possible for a child sim, but it is sparking all sorts of ideas that I can do with a child sim. Family hopping has huge potential for all sorts of gameplay!