First and foremost trust your gut instinct, if something seems not to be right it usually is. Does the child have any unusual bruises or discoloration that seems out of place? Are there any infection that can't be easily explained away? Does the toddler seems to be fussy around a particular person if so pay close attention
There are several signs of the symptoms of toddler molestation. If you see the child repeating the actions to other children or other adults that is the first sign. Also, the child will be afraid to be left alone with anyone. Another symptom is if the child is bruised or red in the private area.
Was there any change (good or bad) in how the toddler acts towards the suspected molestor? Has the child shown any odd behavior for a child like grabbing at the suspected molestor's or anyone elses genitals knowing they're genitals?
If your toddler is able to talk, ask them. Explain to them that it's not okay for anyone to touch them in a sexual manner. You can bring your child to his/her doctor and they can do a check up to see if your child was molested. In the meantime keep him/her away from the suspected abuser.
Toddlers who are very afraid of an adult for no reason is one sign of toddler molestation. They might also say that they were touched somewhere that is inappropriate.