Thanks for your query
The appearance of your 3 month old kid's could be due to allergy
caused by some kind of plant, pollen or animal dander etc in your garden.
Keep your baby indoors for a while and you can get Her/his Ig G levels done.
This test will help to find out if the baby is hypersenitive to various allergens or not.
hope my answer is of some help to you.
Hope to hear from you the follow up report.