PLEASE BE CAREFUL!!! Take this as a warning that a curious little kid or toddler can and will be able to get into almost any packaging. And please take the threat seriously. Contact a local hospital or board of health and go online for more information about tox lines, prevention, first aid. This is not a one-time occurrence but a wake up call to parents!
Unlikely to harm! May be slightly sedative because of size, but very likely not to harm!
No worries. I'm more worried that you would ask such a question here; questions like this need to be phoned immediately to a local poison control center or emergency department. However, Claritin (loratadine) has been shown to be safe in much higher than the recommended dosage in clinical trials, so this shouldn't be a problem. But you already know this, because enough time has passed since you asked it!