Honestly, I don't know what the trends are or will be in summer clothes among teens and adults. But what I can tell you is this: Wear cotton-made clothes. They're cooler, less itchy, and way more eco-friendly than polymer stuff. If you can't get 100% cotton, then compromise with half-and-half clothing, like cotton and hemp.
Adults can go by with skimpy clothes. We'll just slap on some sunblock and we're good to go. But, little kids, especially toddlers, may need a little cover-up because the sun can be harsh on an infant's skin.
I've a two-year-old niece and we dress her up in either a Minti sundress or a pair of Munster shorts matched with a cotton blouse. We also put some sunblock on her and make sure she's protected under an umbrella wherever she goes.