Coldsore on a 22 month old :(

[Tyson86]

Hi my ds has developed a coldsore and im a little irratated as dh and I have not kissed anyone with a coldsore and only my sister that im aware of has then kissed my ds, i found out after she kissed him.
Im very uneducated on this and am worried as i dont want no-one daring to kiss him ever and have no idea what to put on it as the normal coldsore cream doesnt seem to have an age on it IYKWIM.
I feel like he is going to be stuck with coldsores now for the rest of his life and treated like a leper when he has one, im so pissed off at my sister atm.
Please someone tell me how wrong and silly im being.

Are you sure it's a coldsore? You can get impetigo round the mouth which looks loads like a coldsore. For that you need antibiotic cream I think.

Im no way sure, from what my mum said it didnt start off like a coldsore, she said they start off with a spot, this started as a rash, similar to a wet eczema rash but thursday had 2 little white spots in it and yesterday and today had gone tinged yellow IYKWIM. Still red though at the same time.
Im confusing myself now.