"Since they had a child, they have not been the same."
Translation:Depuis qu'ils ont eu un enfant, ils ne sont plus pareils.
Agreed, this is a particularly difficult sentence that you can make so many different grammar mistakes on. - use of depuis qu, ne sont plus, and the proper use of compound tense in the subordinate clause, and present tense in the main clause. Ive been over and over this one. So don't feel bad.
"What is the difference between les memes & pareils?" That is also my question, and it seems to be difficult to answer. https://forum.duolingo.com/comment/16980941/M%C3%AAme-vs-pareil https://forum.duolingo.com/comment/1286720/C-est-toujours-pareil As far as I can guess from looking at various websites, meme = same and pareil = parallel, comparable or similar, but there seems to be a slight grammatical difference, mentioned here: https://www.kwiziq.com/questions/view/what-is-the-difference-between-the-use-of-le-la-meme-and-pareil that meme is an adjective describing a noun (chose, for example), while pareil is an adverb that describes a verb (etre, for example). Hoping someone who actually knows might add to or correct what I have gathered here...
The problem for English speakers is that the words same or the same can have more than one meaning, but no-one stops to think about the exact meaning. In French these nuances of meaning are represented by different words. Rather than learn grammatical rules,the easiest way to know which one to use is by thinking which words you could use to replace 'same' in the English sentence. If you mean identical, the very same, that exact one, then use 'même'. If you mean like it, like this, like that, equivalent, equal, then use pareil. Think about this sentence...'The same man opened the door, but he was not the same.'
With "avoir" as the auxiliary verb, the participle agrees with the object, not the subject, and only if the object is placed before the verb. Look at the object of "ont eu" here: "un enfant". It comes after the verb, so there's no agreement. It must stay as "eu". (Ils has nothing to do with this agreement.)
"Depuis" is a preposition, and "depuis que" is the conjunction. In other words, you need the conjunction if you need "since" + subject and verb. This pattern is true for many other prepositions and conjunctions: après, après que, avant, avant que, pendant, pendant que, etc. So indeed, you would need "que" in a clause.
- depuis 2001 = since 2001
- depuis que je la connais = since I have known her
- avant mai = before May
- avant que ma mère revienne = before my mother comes back
"Depuis" in French is used with the present tense to indicate an action that started in the past and is still happening in the present. In English, you would focus on the past (have not been the same), but in French, the focus is on the present because the action is still happening in the present.
If you have some time, read this explanation about "depuis":