Sure. There's one where Naruto discovers magic in a world that is a blend of the Naruto universe and a medieval magical world. He is transported there accidentally and has to learn magic to survive. The unique part is that his ninja chakra is somehow related to the magic energy there, and he has to figure out how to make them work together.
In some fanfictions, Kushina might find Naruto in a state of self - doubt. She then becomes his source of motivation, reminding him of his strength and the importance of his role. This could lead to Naruto regaining his confidence and achieving great things with Kushina by his side.
There might be a fanfiction where Naruto discovers magic through an ancient scroll. This scroll was left behind by a powerful mage long ago. As he deciphers it, he starts to understand the basics of magic, like elemental magic, which he then tries to incorporate into his combat style. It makes for an exciting read as he experiments and sometimes fails hilariously.
It could be Naruto himself. As he grows and faces new challenges, he might stumble upon these secrets, either by accident or through his own determination to learn more about his world and his place in it.
Obviously, Harry Potter himself is the central character. Then there's Dumbledore, who might be even more vigilant in protecting Harry earlier due to his early magic display. Hermione could also be involved, perhaps being even more intrigued by Harry's early magical experiences and trying to study them.
In some fanfictions of 'harry discovers magic early', he might accidentally perform magic in front of the Dursleys much earlier than in the original story. This could lead to either extreme fear or a strange kind of acceptance from them. Maybe they try to hide it from the wizarding world for their own gain. For example, Vernon might see it as a way to make money if he can control Harry's magic.
Obviously, Harry Potter himself is the central character. Then there are often the Dursleys, who would have to deal with Harry's early magic in different ways. Sometimes, Hagrid might also be involved earlier, coming to rescue Harry from the chaos caused by his early magic manifestations.
One interesting scenario could be Harry accidentally performing magic in front of the Dursleys much earlier than in the original story. For example, he might make Dudley's pudding float right in front of their eyes, which would lead to a huge commotion in the household.
It's possible he gains enhanced physical abilities like super strength or speed. Since his heritage is often tied to some special genetic traits, these could be unlocked upon the revelation. For example, if his heritage is linked to a powerful clan, he could inherit their natural combat prowess. He could also find out about special chakra control abilities that are exclusive to his bloodline, which would give him an edge in battles.
He could uncover the truth about his father's real mission before he died. Maybe it was something that was kept hidden from the village for some reason.