my day today

this morning I have looked after three childrens; I have came took them to the school, and I have gone then went to the work. I work in the state school, and today the pupils have been were polite.
Besides, In the afternoon I've gone I went to look for my nephew. We have eaten drank chocolate and afterwards we have played.
Now, I am going to have dinner and then I am going to sleep.

Ok, you needed to use simple past tense, not the present perfect tense

Use the Simple Past (usually [Verb + -ed]) to express the idea that an action started and finished at a specific time in the past.

"We use the Present Perfect [has/have + past participle] to say that an action happened at an unspecified time before now. The exact time is not important. You CANNOT use the Present Perfect with specific time expressions such as: this morning, yesterday, one year ago, last week, when I was a child, when I lived in Japan, at that moment, that day, one day, etc.

My day today

This morning I  have looked after  watched ( or "cared for") three children at have came the school and I have gone to the where I work. I work in the state school, and today, the pupils have been were polite (or "well behaved"). In the afternoon after work, I I've gone went to look for my nephew. We have eaten ate chocolate and after we have played.
Now, I am going to dinner and afterwards, I am going to sleep.

This morning I watched ( or "cared for") three children at the school where I work. I work in the state school, and today, the pupils were polite (or "well behaved"). In the afternoon after work, I went to look for my nephew. We ate chocolate after we played (or "we played first and then ate chocolate"). Now, I am going to dinner and afterwards, I am going to sleep.

my day to day

this morning I have looked after three children(s), I have came to the school and I have gone to the work. I work in the state school, and today, the pupils have been polite.
Besides, in the afternoon, I I've gone to look for my nephew. We have eaten chocolat and after we have played.
Now, I am going to dinner and I am going to sleep.