Agree with you here, My niece loves them too!
Yes, DC Super Hero Girls is a great series and I hope we get those issues with DCUI!
No, definitely the '60s Gil Kane/Carmine Infantino/Julius Schwartz/John Broome stuff
I started out with mainline comics when I was 6/7, and I turned out just fine… oh, wait
Some examples
Supergirl
https://www.dcuniverse.com/comics/series/-/0f6ce1fe-94cb-4659-beb1-7e497d550ca7
Legion
https://www.dcuniverse.com/comics/series/-/8024e1bf-d03d-41c4-bae3-db15a1b43e74
Billy Batson
https://www.dcuniverse.com/comics/series/-/d53e79df-a2f5-4f76-a01a-f7931e328425
Justice League Unlimited
https://www.dcuniverse.com/comics/series/-/a4932838-b4f4-4efb-a338-226adca883b9
Bat Shark Repellent! I legitimately loved that as a kid.
Speaking of Supergirl and Legion of Superheroes, all of the Golden Age and Silver Age Adventure Comics on here are great for kids.
Super Friends
Young justice!!
The original
Young Justice
By Peter David
Is very kid friendly
It starts as all boys
Then gets
Three female characters
The mothers
Of Wonder Girl and Arrowette
Are not represented well
Though
I’m not sure about comics but I know for sure they should watch young justice season 1 and 2 but not 3. At first when I started watching them I thought it would be some kiddy show but now I rewatch em ever few weeks just for fun.
I will second Super Friends, both volumes. The 1976 volume and the 2008 volume which can be both found on DCU.