1.) a 1 cup or a 2 cup measuring cup (If you feel it would be easier for your learner to pour ingredients by already having the ingredients measured out in measuring cups, it is easier to use both a 1 cup and a 2 cup measuring cups or three 1-cup measuring cups.
2.) 2 cups of cornstarch
3.) 1 cup conditioner - Sauve is a cheaper brand to use for this 
4.) bowl to mix
5.) spoon
6.) optional wet ones to clean hands easier 

Optional but it makes it extra grinchy! :) Links are below for ones you can buy online.
5.) red glitter, green glitter, or red hearts
6.) red hearts

Red Glitter Tube: https://www.walmart.com/ip/Horizon-Group-Red-Glitter-Tube-1-Each/37117827

Green Glitter: https://www.walmart.com/ip/Sulyn-Extra-Fine-Glitter-for-Crafts-Emerald-Green-2-5-oz/36794407

Red heart glitter: https://www.etsy.com/listing/1055896871/red-holographic-heart-shaped-glitter-3mm?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=red+glitter+heart&ref=sr_gallery-1-18&variation0=2157604497

Red heart(s): https://www.etsy.com/listing/1068030090/12mm-red-glitter-resin-heart-cabochons?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=red+glitter+heart&ref=sr_gallery-1-3

Another red heart option: heahttps://www.etsy.com/listing/839115073/16mm-heart-glitter-red-flatback-resin?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=red+glitter+heart+resin&ref=sr_gallery-1-1&organic_search_click=1&cns=1

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