Translation:Children go to school to learn things.
The verb "ir" is indirect transitive, so it requires a complement iniciated by a preposition, in this case the preposition is "a", and then, it comes the article "a", which is optional, but if you choose to use it, there is no way you write "...vão a a escola...", so the correct form should be "...vão à escola...". Don't freak out, this is a very complex topic, even for native speakers.
Sorry, I made a mistake. In this case the usage of the article is required, the only cases it is optional is in front of proper noun, possessive pronouns and after the preposition "até" followed by a feminine noun.
-"Entreguei o presente à Alice" OR "Entreguei o presente a Alice." -"Fui à sua aula ontem." OR "Fui a sua aula ontem." -"Vou até à praia." OR "Vou até a praia."
In any of these cases THERE IS NO CHANGE OF MEANING, so when it comes to optional articles and crase it is all about writing rules, never meaning.
The article rules are a little hard, there are lots of exceptions.
For "à escola", we always use it. But English prefers not to use when it's about going to school.
About "vou até à praia", that's not allowed, because you are using two prepositions (até and a).
You can say both "vou à praia" and "vou até a praia", but not "vou até à praia".