70's children clothing and 80s teen clothing

Onyx sims has 70s clothes but, it may be too realistic for you: http://sims4nexus.com/?p=14565
As for MM, there isn't anything specialized. I was a kid in the 70s and the boys wore t-shirts and jeans (just levis). Brown, orange, avocado, and gold were really popular colors. Striped tees for boys were in.

Do you have any suggestions for the 80s? or is this picture good enough: https://i.imgur.com/84S3nPE.png? (some people say the outfits don't look 80ish - but the tank top does look 80ish to me

For 80s:
Female Workout - https://sims4customcontent.tumblr.com/post/125061179219/i-saw-some-video-that-had-some-interesting-80s
Male Tops - https://saartje77.tumblr.com/post/184045325339/took-me-forever-but-here-is-my-80s-pack-arcade
80s Inspired Earrings: https://someone-elsa.tumblr.com/post/633613417292414976/8-0-s-i-n-s-p-i-r-e-d-e-a-r-r-i-n-g-s-part-1
Farrah Hair: https://ts4decadeschallengecc.tumblr.com/post/656249825441021952/simstrouble-mirela-by-simstrouble-base-game

Here's some children's pants that remind me of what many kids wore in the 70s. (Love the stripes!)
sims4nexus.com/?p=14565
https://thesimsresource.com/downloads/details/category/sims4-clothing-male-child-everyday/title/kids-pants-rpl61/id/1514767/

Here's also some bellbottoms for children ( sims4nexus.com/?p=14565 ) and toddlers ( http://sims4nexus.com/?p=14520 ) .
But I think bellbottoms were only for teens and adults back them.

Here's some more clothes kids would have worn in the 70s.

Blue Jean vests are great. Denim jackets were very popular in the 70s, even on children.
These are great because they go in an accessories slot, so the kids can wear them over any shirt you want.
sims4nexus.com/?p=14184


I also have a link to non-denim vests that are used as accessories here:
sims4nexus.com/?p=12008


This dress looks so 70s girl.
sims4nexus.com/?p=15102
See the shape of the dress, the belt, the plaid. That looks very 70s child!

http://sims4nexus.com/wp-content/uploads/2020/01/Image22-750x450.jpg


This top looks 70s teenager, but I don't remember if children wore these or just teenagers. It might have been considered "too mature" for kids.
https://sims4nexus.com/?cat=162

There's a bunch of very authentic children's 70s stuff right at https://thesimsresource.com/search#/?q=Retro%20ReBOOT%2070s%20children&g=4&p=1

I love the ugly, er I mean "groovy", boy clothes. This type of stuff was very popular on little boys.

https://sims4downloads.net/wp-content/uploads/2021/03/Retro-ReBOOT-70s-Pants-for-Child-01-sims-4-cc-600x450.jpg

Jumper dresses for toddlers.
https://mystufforigin.com/ep09-dress-sweater-for-toddlers/
https://www.mystufforigin.com/wp-content/uploads/2020/07/GClothes-1-1000x817.jpg

Now onto the 80s teenagers.

Here's some looks that were popular with teenage boys. It has a variety of authentic tops.

https://saartje77.tumblr.com/post/184045325339/took-me-forever-but-here-is-my-80s-pack-arcade


These ski jackets would have been popular in northern states.
https://patreon.com/posts/vintage-jacket-26395956


Here are a couple of 80s lookbooks , with a variety of different styles that teenagers of different social groups would have worn:
https://emmastillsims.tumblr.com/post/185243382275/decades-lookbook-the-1980s-this-lookbook-was

https://emmastillsims.tumblr.com/post/629096319161614336/decades-lookbook-1980s-part-2-the-1980s-were

Here's one of the most popular hairstyles of the early 80s, the Farrah Fawcett look.
https://thesimsresource.com/downloads/details/category/sims4-hair-hairstyles-female/title/farrah-hair/id/1503656/
https://www.thesimsresource.com/scaled/3177/w-920h-690-3177078.jpg

This looks pretty 80s teen.
https://descargassims.tumblr.com/post/167801405977/lookbook-challenge-5-80s-hair-sweater-pants

https://64.media.tumblr.com/428db7d995cf17063c18af43ff4654df/tumblr_ozvim26D8i1tv0gg3o1_1280.jpg