Bedding type?

Hi guys, I posted a minute ago and my phone freaked out and froze so my apologies if I posted twice.

I have 2 bunnies that I got at 2 days old because they were orphaned. They are 3 weeks old now and I have been using blankets as bedding. What should I put in their litter box? Shavings? Is their a certain type or size. Will they choke on them? I found out they are Himalayan x double maned lionhead. They are really adorable and I hope they continue to do well. They have milk replacer crusted on them that I can't get off!!

Blankets are fine.
Keep an eye they dont chew at them as for litter for the litter box. Use wood stove pellets. Usuallu 5 or so dollars for a 40lbs bag at tractor supply stores or walmart or home depot type stores. Really helps with any smell as well.