Can loratadine cause children to have violent mood swings and suicidal thoughts?

Maybe: In rare cases, yes. But not likely.

Seems unlikely: Odd reactions to medications do happen, but this would be unusual. Still, if you are worried, there are other medications to help with allergy symptoms, so ask to switch to something else. Any effects of the type you describe, if caused by loratadine, should go away when you stop it.

Unlikely: However if it is Loratidine-D (with pseudoephedrine as a decongestant) yes, it can cause mood swings, hyperactivity, possible agitation and insomnia. Loratidine, when taken as directed for allergies - is one of the safest treatments known. There's no evidence of harm to a fetus when a pregnant mother takes it, or when breastfeeding taking the plain loratidine.