Your 7 year old being into a cartoon with people in spaceships using jets that turn into robots and fire missiles by the hundreds to fight giant aliens surprises you?

Disney doesn't own Robotech yet? They're slipping...

None of the Robotech productions based on Harmony Gold's original stories (i.e., all the sequels) are all that good. Sentinels wasn't even completed -- they only finished the first three episodes, which were pretty mediocre. I read the novelizations of the Sentinels series, and it got really weird as the series progressed. The fact is that HG hasn't been able to produce a single decent Robotech production that wasn't an adaptation of an original Japanese production.  Don't get me wrong -- I was big Robotech fan as a kid, and to a certain extent I still am. But these days I'm more of a fan of the Macross franchise (though I still have a soft spot for Mospeada).

As far as the Macross sequels, in order:

Macross II is considered non-canon as it was produced without the involvement of Shoji Kawamori. Subsequent Macross productions have pretty much ignored and/or contradicted it.  I've seen it and didn't think much of it.  My grade: C

I enjoyed Macross Plus quite a bit, but it's definitely a departure from the Macross formula. While it has some of the elements common to other Macross productions (love triangle, pop singer, hot shot pilots, transforming planes), it's much more of an interpersonal, smaller scale story. It's also much more of an adult story and might not be a good fit for a 7 year old.  My grade: B+

I haven't seen Macross 7, but it's considered the oddest entry in the series.  It takes the Macross trope of using the power of music to defeat the enemy and really runs with it.  The main character is the singer and guitar player for a band, who also pilots a Valkyrie that has guitar controls in the cockpit and speakers built into exterior for blasting the enemies with his music.  Never mind that the speakers would be useless in space.

Macross Zero is a prequel mini-series.  Isn't considered one of the stronger entries, but it gets points for being the first series to use cel-shaded CGI animation for all the mecha scenes, as well as featuring a young Roy Focker/Fokker as one of the main characters.  My grade: B-

Macross Frontier was the last series to be released in Japan.  It's considered the most similar to the original Macross series, and directly homages many aspects of it.  The best way I can describe it is that Macross Frontier homages the original Macross in much the same way that The Force Awakens homages A New Hope.  Of all the sequels, it's the one I enjoyed the most.  My grade: A

A new Macross series is currently in production as well called Macross Delta.  I don't know too much about it though.

I'd try to watch DYRL before Frontier.  DYRL basically takes the story from the Super Dimensional Fortress Macross series and adapts it to a feature-length film.  If your Macross knowledge is based entirely on Robotech and you don't want to have to watch SDFM with the original story intact, it would be a good way to get a crash course in some of the differences between the original Japanese series and Harmony Gold's modifications.  HG's adaptation of SDFM for Robotech is fairly faithful in terms of the characters, relationships, and basic plot.  Where it diverges is the mythology (which makes sense, since they had to create a new mythology that would connect three series that had nothing to do with each other).  As one example, Protoculture in Robotech is a mysterious energy source.  In Macross, The Protoculture is an ancient civilization (Protoculture, i.e., prototype culture) that is the progenitor of both the Zentraedi and humans.  But aside from all that, DYRL is a great entry to the series.  The animation alone is worth it.  SDFM was uneven in it's animation quality, as the studio responsible for animating the show sub-contracted some of the episodes to another studio, and it's pretty obvious which ones.  DYRL looks like the animation that was done by the original studio taken up several notches.

It's also worth mentioning that continuity-wise, even though DYRL and SDFM tell the same basic story, there are some differences, and the sequels seem to take most of their cues from DYRL rather than SDFM.  As one example, the song "Do You Remember Love?" which provides the title for the film doesn't even appear in SDFM, but it shows up in Frontier.

Mobile Suit Gundam is also a worthy series to consider.  Granddaddy of the genre and all that.  The creators of Macross were huge fans of MSG.

Somehow no one mentioned Evangelion? It might be a little too deep for a seven year old, but it definitely had great giant robot action, and the pilots are all pretty interesting characters.

There's Cyborg 009.. that would probably be a pretty good one for that age... fun art.

Gundam has about 8 million spin offs, and I've never been able to really piece it together, but I'm sure there's something in there that would work.

Voltron's a great call, too .. maybe 80s Transformers?

Evangelion is a huge favourite of mine, but even compared to Macross and its contemporary giant mecha shows, it features some content that's excessively violent/disturbing. Maybe more appropriate for a 14-year-old than a 7-year-old, and also easier to appreciate at that age in terms of plot intrigues.

And I say this as someone who watched 'Animals of Farthing Wood' at age 7, which featured violent death of main/supporting characters every other episode.

But again, great great show.