It is possible for a child to have cavities if eating raisin cereals?

It is possible for a child to have cavities no matter what the child eats.  When you mention raisin cereals, I assume you mean that the child is eating that kind of cereal instead of something with more sugar?  Eating raisin cereals may help make cavities less likely.  Even so, it doesn't matter -- people can get cavities no matter what they eat.

First of all, cereal is not all the child eats.  They are eating other meals too so what they eat at those other meals will have an impact on whether they get cavities or not.

It is also very important to think about how the child is caring for his or her teeth.  Children who brush and floss are of course less likely than other children to get cavities no matter what they eat.

Finally, genetics come into it as well.  Some people have teeth that are more resistant to cavities no matter what they eat or how well they take care of their teeth.