Can allergies cause fever in toddlers?

No: You would not get a fever with an allergic reaction. Skin may feel or look flushed, but the core temperature would not rise (thus no fever). If temperature is over 100.4, it is not just allergies, but could be something minor like a virus. Push fluids, have child rest and monitor for new symptoms.

Should not: By saying allergies i assume you mention seasonal your year round nasal congestion due to allergies. It should not cause fever unless there is a bacterial super infection or acute rhino sinusitis. Untreated allergic rhinitis or nasal allergy symptoms will increase risks of having acute bacterial rhino sinusitis. You should take your child for a doctor visit to make sure there is nothing serious.