For the best results for your kids, it's important to provide real watercolor paper and decent paints.

-watercolors: a pan set (please, not tubes of watercolor) - 8 colors is more than enough as they can blend their own! Please note that, offten, the pan sets that come as part of a large art kit with pastels and colored pencils, the kind that that has many, many colors of watercolors in them, have more binder than color and are harder to paint with. I will offer specific suggestions in the classroom.

-9x12 or 8x10 140lb WATERCOLOR paper - please have a pad or stack of it available as we will go through at least 2-3 sheets every day. (Please note, although thick drawing paper can work with watercolors, 'special effects' won't work nearly as well since it absorbs more quickly than watercolor paper. If that is all you have to work with, your student's effects won't be as notable and this paper will in face feel very frustrating for them. I'll offer suggestions in the classroom - it's important to buy watercolor-specific paper that's 140lb weight, not pads that say 'watercolor and marker paper' or lightweight pads labeled watercolor paper, because thick drawing paper or cheaper multi-purpose paper behaves differently.

-brushes - you will need more than the tiny brush that comes with the watercolor set. You definitely need a bigger, thicker brush. You can get nice brush sets for $5-6; I can offer suggestions in the classroom.

-a jar or container to hold water, no more than half-full
-a folded up paper towel or washcloth (on all days - to rest brushes on)
-crayons or oil pastels (either is fine)
-paper towels or paper napkins (for a different purpose)
-tissues
-scotch tape (cellotape)
-plastic wrap
-wax paper
-a very small dish of salt, or a salt shaker (if you have different kinds of salt in your house, like coarse or kosher as well as fine, then provide two different kinds for extra fun)
-OPTIONAL: a cotton ball or cotton pad 
-OPTIONAL: a few q-tips/cotton buds 

Learners will not need to use any apps or websites beyond the standard Outschool tools.

Watercolors can stain! You might wish to provide a smock or already-stained shirt for your artist to wear, just in case. You may also cover your table.

Since I'm requesting that you bring scissors, be aware, of course, that scissors are sharp. I'll remind them to be careful, but if you are concerned about your learner using them, you can stay nearby, off-camera.