Hand foot mouth is a very common illness that most kids get during childhood. It is easily spread through body secretions such as saliva and stool. Although the virus most commonly associated with it is called coxsackievirus there are other strains that sometimes circulate.
I actually like to call it Hand Foot Mouth and Butt, because in my experience kids often get blisters on their butts as well as on the hands and feet.
Some people have mild congestion, sore throat and fever as part of the package.
It is a very variable illness, meaning that one child will not look very sick and another can feel wretched. The lucky ones might simply have a mystery blister on the hand and that is the extent of it! Most of the time the worst symptoms resolve in a week or so.
If your child is running around, has normal activity level, and reasonably wet diapers, then they are "managing" and I wouldn't be too concerned.
On the other hand, If you child has the illness, they are contagious as long as they still have blisters or a fever and perhaps can shed the virus for a week or two afterwards.
If your child is happy and eating and has no fever but has a few blisters I would try to keep them away from a newborn or someone with a compromised immune system, but it seems excessive to expect you to keep your kids out of daycare if that is the only symptom.
Good hand washing is key to avoiding this.
Make sure the shared toys are cleaned frequently.