I'd think an annonomous call to child protective services would help. If there is anything funky going on they will investigate and take proper action. If everything is fine their presence there may cause the mother to take more care. Plus is there an outside chance that's the baby sitter not the mother? In which case I'd think the mother would like to know what's going on.

According to Florida State Law concerning child welfare...


Florida
Physical Abuse § 39.01

Abuse means any willful act or threatened act that results in any physical, mental, or sexual injury or harm that causes or is likely to cause the child’s physical, mental, or emotional health to be significantly impaired.
Harm to a child’s health or welfare can occur when any person inflicts or allows to be inflicted upon the child physical, mental, or emotional injury, and can include:
• Purposely giving a child poison, alcohol, drugs, or other substances that substantially affect the child’s behavior, motor coordination, or judgment or that result in sickness or internal injury
• Inappropriate or excessively harsh discipline
• Exposure to a controlled substance or alcohol
• Engaging in violent behavior that demonstrates a wanton disregard for the presence of a child and could reasonably result in serious injury to the child

Persons Responsible for the Child § 39.01

• Caregiver means the parent, legal custodian, adult household member, or other person responsible for a child’s welfare.
• Other person responsible for a child’s welfare includes:
o The child’s legal guardian, legal custodian, or foster parent
o An employee of a private school, public or private child daycare center, residential home, institution, facility, or agency
o Any other person legally responsible for the child’s welfare in a residential setting
o An adult sitter or relative entrusted with a child’s care