Translation:El niño está contento con su perro.
Both 'feliz' and 'contento' are accepted are correct in this sentence, so are they generally interchangeable?
"Feliz is used for being in a momentary state of happiness (estar) or for being a happy person (ser). "Contento(a) is also for being in a state of happiness but calm and not demostrative. Contento is not quite as strong as feliz but the difference between the two is minimal." Source - spanishdict. Remeber google is your friend.
Es is ser and está is estar, both mean to be, so, ser is used to talk bout permanent actions (ur name, where u from etc) and estar to talk about temporary actions (how u are feeling now, what are you doing now etc). Hope I helped
So whenever someone is happy with something/someone instead of just being plain happy, you use contento/a?
También sería correcto: "El chico es feliz con su perro". Lo he reportado ( 15 / 9 / 18 )
Why is it esta and not este? Perro and nino are both masculine right? Or is esta for both masculine and feminine and este is for something else?
Verb changes DO NOT based on "masculine or feminine" noun. Verb changes are based on "the subjects - like I (yo), you (tu'), he (e'l), she (ella), formal you single (usted); we (nosotros/as) ... you get the picture.
Please note, there are esta (=THIS for feminine; without accent over [a]) and esta' (= IS ' with accent -['] over [a] for he is, she is, usted (formal you singular)).
este = (THIS for masculine)
There are to "to be" (SER and ESTAR) in Spanish. It will take some time to learn how to use them correctly. Don't worry, you will get there.
I hope this help.
I am also a student.