He can go. He has no fever. If mucus is clear then he's fine. Sounds to me that he may be having allergies as it is spring and it is that time of year. Without knowing his age, he need to find some allergy relief meds. Teach him to blow his nose. Some kids catch on fast, some take forever to get it. If he's very little use a bulb to suck out the mucus before you leave. Kids get clear boogies quite often but doesn't mean they're sick. He can go.
mom to 5 including triplets