I agree children need discipline but people get so judgmental and mad when a three year old is having a bad day. Your kids weren't perfect and neither are any one else's! So stop judging a parents parenting based off a one time meeting.
Use a mesh laundry pop-up bag for beach toys, at the beach and home, and keep the sand where it belongs. Also, use baby powder or corn starch to get sand off of skin. Just sprinkle where the sand is and it falls right off!