A Muslim child who died at the age of six, is it permissible to build a mosque for him?

It is permissible, but according to the majority of scholars.

The first thing is that this person is not accountable.

Good deeds are written for him and bad deeds are not written against him. He is distinguished at six years old.

Good deeds are written for him, so there is nothing wrong with building a mosque for him.

But according to the majority of scholars, and some have reported consensus.

On this topic, which is that the children of the Muslims are in jannah.

All of them, and some have said that they will be tested.

On the Day of Judgment, but the most well-known view, and Allah knows best, is that they are in jannah, as long as they are children of the Muslims. In fact, according to the majority, even the children of the polytheists.

If they die before reaching puberty, they are also in jannah. Allah knows best.