Learning to tune a violin (or any stringed instrument) by ear takes a lot of practice, but modern technology gives us some beginner-friendly shortcuts.
The guide below is more for parents, but kids can give it a go too! Take it slowly and be very gentle with the pegs.
There are many similar-looking apps in the Android and Apple app stores that can help with this. The one I like is “Simply Tuner”. It’s available in the Apple and Google stores, it works well and there are no ads.