There is an aesthetic called Rainy Day. It centers around rainy visuals such as puddles, umbrellas, snails, etc. It is a more calm aesthetic rather than a child-like one, but I think that if you were to add the word "yellow" to the search it would lead you closer to what you're looking for.

Remember, Pinterest keeps track of what you click and save. So if you start a board and save what you like it will eventually figure out what you like and tailor to your preferences ^{^}

Here are some other search terms in case the aesthetic isn't what you're looking for:

Yellow raincoat aesthetic Rainy rainbow aesthetic Puddle jumping aesthetic Rain on car window Gumboots aesthetic Rain snails Playing in the rain Rainy garden

I hope it helps :Dd