July on Corfu is hot (see the link below for last year). Temps can be up into the very high 30c, and into the 40s. However, we normally holiday in late July and into August (still very hot), but we have seen families out there with small babies of a similar age.
The obvious is to ensure that they are protected and shaded well, with lots of fluids on hand for them to drink. You can get baby suits I believe for full protection but at the same time they keep baby cool as well. Probably a bit over the top, but a good SPF Sun Cream like P20, or the highest sun cream you can get will ensure baby and everyone has a good time.
Remember, protection from the sun (particularly the afternoons), and lots of fluids for drinking.
I hope this is helpful for you.