I just read through the lyrics. To my best guess, when Twilight sings "You have my little ponies". It's right after the mane 5 say their lines, so saying "You have my little ponies" to me, sounds like an introduction to the group. The best example I can come up with is, imagine 2 people in a boxing ring. The announcers will say "In this corner you have boxer number 1".
The fact she says "Don't you know you're all my very best friends?" after that verse it makes what I say make more sense. After introducing the gang "You have my little ponies", you then get her telling them they are her best friends, "Don't you know you're all my very best friends?".
Another possibility would be that it's literally just summoning up the bases of the show and what it is. They say "big adventure" which you get lots of adventures in the show. They say "tons of fun" which they have a lot fun in the show. They say "A beautiful heart" which most of the ponies do. They say "faithful and strong" which the ponies are in fact, faithful and strong. They say "sharing kindness" which is a trait most of the ponies share and lastly they say "and magic makes it all complete" which a lot of ponies have. This whole part of the song sums up the show and the ponies themselves. This is followed up by "here you have my little ponies", this is the song introducing you to the show and the pony universe that is My Little Pony. When she says "do you know you're all my very best friends?" it's just her saying all of the ponies and you as well (the viewer) are her friends.
In my opinion it's probably the second possibility. The song, when analysed and read in English terms, sounds to me like 1 big introduction. Considering it's the theme song that plays before anything starts would suggest that the song is just introducing you, as opening themes are more or less an introduction anyway.