"Se souvenir" is a reflexive verb and like all reflexive verbs (also known as pronominal verbs), it uses être as an auxiliary verb, not avoir. https://www.thoughtco.com/etre-verbs-french-auxiliary-verbs-1368843
"Se souvenir" is one of a number of French verbs which are termed "reflexive", i.e., the action of the verb is on the subject of the sentence. This is shown with the reflexive pronoun which precedes it. It seems odd to us in English because we just say "They remembered..." but in French, the verb must be used reflexively. http://french.about.com/od/grammar/a/pronominalverbs.htm
There is a list of about 24 verbs which use être. Listed here: https://www.thoughtco.com/etre-verbs-french-auxiliary-verbs-1368843 Those are sometimes referred to as "verbs of motion" but as you can see, they are not all necessarily about motion (naître, mourir) and there are other verbs of motion (e.g., marcher) which do not use être. In addition to this list, all reflexive (pronominal) verbs use être as the auxiliary verb, not avoir.
I can provide all kinds of information to you but you may want to pace yourself as you process it. Reciprocal verbs are those where two or more subjects act on "each other". These work just like reflexive verbs and therefore will use être as the auxiliary verb. I suspect you have already looked up this information. Now you need to grapple with it until you have it all figured out. https://www.thoughtco.com/french-pronominal-and-pronominal-verbs-1368926 You will find more answers than you have questions on the thoughtco.com site.
Google translate is perhaps not a reliable source of translations. Try one of the online dictionaries:
- WordReference: http://www.wordreference.com/fren/
- Larousse: http://www.larousse.fr/dictionnaires/francais-anglais/
- Reverso: dictionnaire.reverso.net/francais-anglais
- Oxford: www.oxforddictionaries.com/translate/french-english
- Linguee: http://www.linguee.fr/
- Linternaute: http://www.linternaute.com/dictionnaire/fr/
You know that it is enfants rather than enfant because of the following:
their child is leur enfant
their children is leurs enfants and there is a liason between the s of leurs and the e of enfants.
In the recording you can here the liason.
Note that the consonants involved in liaison generally include d, s, and x. However, their pronunciation is changed so that s sounds like a z
vous avez is pronounced vu-za-vay
se souvenir is an intransitive verb so it cannot have a direct object. Therefore, the construct for using se souvenir is:
se souvenir de quelque chose
Je ne me souviens pas de sa response. - I cannot remember his answer.
Je me souviens de vous - I remember you