(My experience here is from the school psych suggesting ADHD for my DD, and neuropsych testing suggesting that she does not have ADHD)
Your kids are really young. Really young. Younger than most psychologists would be willing to diagnose ADHD, particularly in a boarderline or more complicated piece.
What testing went into the diagnosis? What's the learning disability? How severe?
Proper testing with a tester experienced with kids that age should be able to distinguish "bored" from ADHD pretty easily.
HOWEVER, processing speed and working memory significantly below verbal and perceptual skills (assuming WISC/WISPII here) are generally taken to be an indicator of ADHD. However, many gifted kids are verbally gifted and gifted in perceptual/spatial skills without the Ferrari engine (high WM/PSI) driving all of it. So it can lead to some confusion in the diagnosis if the diagnostician isn't experienced with gifted kids. This becomes a bigger problem with the more gifted the child is. You can calculate the general abilities index (GAI) from the WISC subtests and compare it to the FSIQ to get a sense of how big of an issue it is. In my DD's case, the difference was "just" 15 points, and this was considered a factor of how gifted she is, not that the WM/PSI were deficient.
Observation during testing can be revealing, as can the parent/teacher/coach surveys, and other testing (DD took the IVA -- this is torture and should be banned by the Geneva Convention -- and the NEPSY) can also inform the diagnosis.
Throwing a learning disability into the mix complicates things. ADHD is a diagnosis of exclusion: You can only count behaviors not otherwise explained by the learning disabilities or an inappropriate learning environment. As an extreme example, my DD's behaviors in math were attributed by the school psych as ADHD. We decided later (with the neuropsych report in hand, and a vice principal fully brought into the loop) that the problem was that DD's math environment was not conducive to either concentration or engagement. Solving the noise distraction issue and solving the lack of instruction issue eliminated the ADHD-like behaviors.
If you are skeptical of the diagnoses, then address the behaviors and learning challenges as they come up, continue to watch and observe, and return to it in a few years when you have more information and the kids have grown up some.
When it comes to keeping the kids happy and engaged, this is the $64k question, right? And it's the right place to focus your attention IMNSHO. First things first: Is your DD's learning disability being addressed effectively? That should be first on the agenda, as this can throw up blockades in all aspects of life. If she's in school, then you should approach the school with the testing results, be upfront about your skepticism on the ADHD diagnosis, and ask for their teamwork in addressing your daughters talents alongside her deficits.
Good luck. You are addressing these things really early. You are lucky and smart to have caught learning disabilities in such a young child. Early remediation is key.