A majority of the prominent Marvel superheroes are either adults (such as Captain America or Iron Man) or beings whose age is much higher than humans could ever dream of (Thor). However, there are also super-powered strong children who have left their mark on the Marvel universe.
Some of them discovered what they could do relatively soon, others waited a while before they decided to follow in the footsteps of older, more experienced superheroes. Regardless of how long it took them to put on the costume and start fighting crime, it's inevitable that some Marvel children are stronger superheroes than others.
5 X-23
While not as strong as other child superheroes, Laura aka X-23 can't be accused of lack of powers. She shares many powers with Wolverine which makes sense considering she's a female clone of him. That means Laura has the power to heal her injuries, making her as close to immortal as they come. She has other typical superhero powers, such as super speed, strength, agility, and superior reflexes. Considering how strong Laura is, it's no wonder she has already made an onscreen debut even though she only premiered in the comics back in 2004.
Laura played an important part in Wolverine's farewell movie Logan (2017), and despite being a child when the story took place, she held her own in multiple fights. Considering the Marvel's tendency to introduce legacy heroes, it's not such a stretch to imagine Laura could play an even bigger part in the movies in the future. She's not yet as strong as Wolverine is, as proved by the fact that he won most of the time when they fought, but she has a promising future ahead of her.
4 Spider-Girl
Spider-Man is one of the most beloved superheroes among the fans, and his popularity led to the creation of multiple spider-people. One of them was none other than Mayday Parker, the daughter of Peter Parker and Mary Jane Watson. May inherited her father's powers and became a superhero known as Spider-Girl even though her father was against it.
Spider-Girl has powers similar to Spider-Man - that means she's super strong, agile, can sense danger in advance, and, of course, move around the city thanks to her webshooters. Her strength index is in the 50+ tons category which makes May one of the stronger younger superheroes but yet nowhere near as strong as her father. She also doesn't have as much experience as Peter Parker does, but this is something that could change in her future stories.
3 Wiccan And Speed
The two brothers can fit in a single category since they're both Scarlet Witch's children. As for their powers, Wiccan can manipulate reality and use magic just like his mother does. So even though he isn't as physically strong as other superheroes are, his magic powers make it easy to overlook this fact. As Speed's name suggests, his main power is super speed. It's not clear how fast he is but at the very least, Speed can achieve at least Mach 4.
Overall, the brothers' powers complement well, and make them stronger together than they are when they work on their own. The brothers have already appeared in the MCU, most notably in WandaVision, and showed their power, but the MCU has yet to show what they can really do. One alternative is that Wiccan and Speed could join the Young Avengers in the MCU, just like they did in the comics, and work alongside Ms. Marvel, for example.
2 Franklin Richards
When a child's dad is Mr. Fantastic and his mom is the Invisible Woman, it's almost guaranteed that the child will end up immensely powerful. Franklin Richards is a good example of that. He has psionic powers and can manipulate reality, making him even more powerful than both of his parents are. Just for comparison, another Marvel superhero who can manipulate reality is none other than Scarlet Witch, and everybody knows how much damage she could do if she decided to change whatever she didn't like about the world.
For example, Scarlet Witch managed to erase about 90 percent of all mutants' powers with a single sentence. So if Franklin followed in her footsteps, he could be a genuine threat, but also a force to be reckoned with if he used his powers for good as an adult. If that wasn't enough, other than the two base powers, Franklin has a list of powers longer than Captain America's morning run, making him one of the strongest young Marvel superheroes.
1 Skaar
One of the lesser-known Marvel characters, despite his strength, is Skaar, Hulk's son who appeared in the Planet Hulk storyline. Considering Skaar's parentage, it makes sense that he's not only extremely physically strong but has a lot of other powers at his disposal. If that wasn't enough, Skaar inherited even more powers from his mother Caiera.
As a result, he heals fast, is resistant to cold and electricity, among other things, is practically immortal, can absorb radiation and control it, can breathe underwater, and even turn himself into stone, among many other things. The only luck is that Skaar has yet to play a major role in the main Marvel universe. Because if he did show up and decided to fight the heroes, they would have a hard time dealing with Skaar, despite the fact that he's nowhere as old and experienced as his father when it comes to fighting.