I'm getting a ukulele for a child and was thinking of getting a plastic rather than wooden one as they are said to be more durable and have better tuning stability and intonation than cheap wooden ones. I will also get her a clip on tuner. My question is, do clip on tuners work properly with plastic ukes? Given that they have hollow headstocks, I'm not sure if there's enough mass for the tuner to pick up the vibrations.
I want to commend you on providing a child with a musical instrument and encouraging them to learn to play. Ukelele is a good first instrument for a child. Hopefully the seed of inspiration you are planting now will lead to a lifelong pursuit of music and musicianship.
Yes a clip on tuner should work just fine on a plastic uke. The are extremely sensitive and pick up even very weak vibrations.
I think you will be fine clipping it on the headstock on just about any plastic uke and getting enough vibration for the tuner to sense. I like Snarks but any good clip on tuner should work.
There are also good inexpensive tuners that have a microphone so vibration is not needed - but try an inexpensive clip on first. I am sure it will work just fine and they are easy to use.
Some ukes have a bridge that will accommodate some clip on tuners, so you could clip the tuner on the bridge if for some reason it was not picking up enough vibration from the headstock.
And if you got a uke like the one pictured below - you could even clip it on the edge of the soundhole.
"Yes" is short answer.
My clip-on tuner will detect vibrations in my electric guitar which has no resonant cavity. I also don't think the hollowness will reduce vibration, I rather think it might lead to greater resonance even?
The other thing to note is that many clip-on tuners let you switch between vibration and microphone, I would strongly recommend getting one like that (Snark for instance) which would remove the problem even if it did occur!