By Leroy Leo (Reuters) -The United States has begun distributing COVID vaccines for children as young as six months around the country, and availability of the shots will improve in the coming days, according to White House COVID-19 response coordinator Dr. Ashish Jha. U.S. regulators authorized Moderna Inc’s two-dose vaccine for children aged six months to five years and the Pfizer-BioNTech three-shot regimen for children aged six months to four years late last week. It is unclear how many parents will vaccinate their youngest children. Just one-in-five parents with children under age five sa…