Hello Commet,
Here are few things I saw in your translation.
Attention tout de même, je ne fais que des propositions de correction.
Il vaut mieux que tu attendes d'autres avis éclairés sur ce forum, et je te rassure, il y en a !
(Mon bla-bla est en italique si je n'ai pas raté ma manip)
I recommend Nadia to you "which was occupied of my 4 year old son for 5
months" :
"who took care of my 4 year old son for 5 months"
"Nadia adores the children" : "Nadia adores children"
"It is" : She ... Nadia is a She. "It" is for things (choses) and animals.
so :
"It is very attentive with their needs and it has an easy contact with them" :
"She is very careful about their needs and goes along so well with them"
"It is an attentive girl and serious" : cf. plus haut
"She occupied herself very well of my children, she read
stories to them, she played with him and helped it to progress to the
school".
"She took care of my children so well, reading them stories, playing with them and also helping them to progress at school"
"Moreover, it is a person very pleasant, worthy of confidence
and informed about the responsibilities for the children"
"Moreover, she is a trustworthy and good-natured person, aware of responsibilities required for childcare"
"It also helped me in the domestic spots, to clean the house, to pass by again
clothing of small and to make races"
"She also helped me with the housework, cleaning the house, ironing the little ones' clothes along with some shopping"
"I encourage it to go to England because I know that that will be a very good experiment for it"
Replace "It" by "Her" in this sentence. Also, replace the second "That" by "It"
"You will be able to note that Nadia is an obliging girl, generous and open
of spirit"
"You will see that Nadia is an obliging, generous and braodminded girl"
Je n'ai pas vu d'équivalent de la dernière phrase dans le texte traduit, alors je me lance :
"She is very eager to learn about English culture and wishes to become fluent in English. Undoubtedly, you will not be disappointed"
Sincerely.
En espérant que cela aide / Hoping this helps. 
Droops