MOst towns have pre schools, for children up to the age of 6, and some have pre shcools attached to the main school, although places here are limited as it is not a legal requirement, the earlier you apply the better your chances of getting accepted are. If you are over before you actually move I would advise you to visit the school and enquire. If there are no places at the pre school attached to the school there is quite often a fee paying pre school. It ususally costs approx €90 per month. You also have to buy text books. As fa r as standard of reading and writing at that age goes that is a tuff one as each child is different, my daughter whgo is seven was average in the UK and is still average here (although she cannot understand ALL she reads, she can read it all, which in the Uk she couldnt, but that is because once you have learnt the spanish alpahbet you can read any thing as the pronounciation doesnt change).
Our children could say hello, goodbye please thankyou and count to ten plus a few colours when we came to live here, the first few days were difficult but they got by (there are no english speaking teachers at my daughters school). Because we have no school bus from our village the children can - and ours do, stay at the convent in town during the week - free of charge - and this has helped them immensly, as they have spanish 24/7 for 5 days a week, even the first weekend they came home we noticed a remarkable differnece in their spoken spanish and when they got theri homework out we were amazed, they only had to ask me two or three things - and my son is 13.
WE now have to remind the childrn to speak english at home and encourage them to watch Uk vifeos at least once a eek to keep up their english as we want them to be bilingual. In fact aftr three months at school my sons marks were the saem for english as spanish!!!