Wa alaykum salam,
No. They won't go to hell. We are not accountable until the age of puberty.
First and most important thing you need to understand is: This world is a test. Every single little aspect of life is a test. Allah will try people from childhood till old age.
If a child under the age of accountability dies, he goes straight to jannah.
Second and important principle that needs to be understood: Allah is Most Wise. This means there is always a purpose behind everything that happens. Good or bad. As an example, a person might be on his way to a once-in-lifetime tryout session for football, but he could trip over something and fall requiring an immediate hospital check-up. At the check-up, the doctors might find this person has a serious illness that if left unchecked would result in that person dying soon. I hope you can now see the wisdom behind that guy tripping in the first place? He may have missed his football practice, but is able to take precautions against the unknown serious illness.
In this way, there is always a reason for everything to happen. Divine wisdom is always at work. A boy's parents could die in an earthquake and leave him behind to be raised by the local mosque run orphanage, exposing him to Islamic knowledge and inculcating in him the yearning to become a great Islamic scholar with the desire to change the world.
I hope these two examples are enough to show that we shouldn't think only of the short term effects. Islam means to submit. What does that mean? It means to resign yourself to Allah's will. You accept the conditions Allah places on you while acknowledging that there is benefit in whatever has happened becasue Allah is indeed Most Wise.
Allah punishes people in this world too for their sins - either because they are terrible sinners and deserve punishment after punishment or because they are infact good people, but Allah wants to meet them on judgement day with them having less sins (hardships wipe away sins).
Allah is also Most Just. Therefore, every single injust act that has ever been committed will be brought to account on the day of judgement.
We need to be long term thinkers. This world and everything in it is so measly compared to the hearafter. We can't afford to lose perspective of the aakirah.
Topic: Malaria