There is high chance.
I have gone through your query.
labialis has several stages. Your husband was at open lesion which is a highly contagious stage. The watery discharge contains active viral particle.
There is a chance that discharge has mixed with soda and your son accidentally drank it and spread over his face.
I will advice you to wait and watch. If any itching starts or reddening of skin over face appears,sore throat
, Consult a local Pediatrician
for anti-viral medicines.
There is no need to worry about it or prophylaxis.
Hope I have answered your query. If you have any further questions I will be happy to help.