What is the word for cute/juvenile features?

You might be looking for neoteny

The retention of juvenile characteristics in the adults of a species

In amine / manga and general Japanese culture this is referred to as kawaii:

Kawaii (Japanese: かわいい or 可愛い, IPA: [kaɰaiꜜi]; 'lovely', 'loveable', 'cute', or 'adorable')1 is the culture of cuteness in Japan.[2][3][4] It can refer to items, humans and non-humans that are charming, vulnerable, shy, and childlike.[2] Examples include cute handwriting, certain genres of manga, and characters including Hello Kitty and Pikachu.[5][6]
The cuteness culture, or kawaii aesthetic, has become a prominent aspect of Japanese popular culture, entertainment, clothing, food, toys, personal appearance, and mannerisms.[7]

In German there's the term Kindchenschema and checking several translation websites they suggest one of the following terms in English (in no particular order):

• schema/scheme of childlike characteristics / childlike schema/scheme (dict.cc, leo.org, linguee.com)
• cuteness [small child pattern] (dict.cc, also backed by wikipedia)
• baby schema (pons.de, also kinda backed by wikipedia)
• baby face (linguee.com)

Sources:

• wikipedia article on cuteness
• dict.cc
• leo.org
• linguee.com
• pons.de