The armed wing of Hamas said it carried out the attack that wounded the boy.
One Palestinian was injured earlier in the day by Israeli aircraft, the military said.
Twelve Israelis have been killed by the rockets in the past six years.'Resolute measures'
David Baker, Israeli government spokesman, said: "Israel will take resolute and decisive measures to protect our citizens.
"We will not allow Israeli families to be victimised by Palestinian rockets in the heart of their own cities."
Israel imposed a blockade on the Gaza Strip, cutting supplies of food and fuel to the territory, in an attempt to get the residents to push for an end to the rocket attacks.
Several countries and human rights groups have condemned the move as "collective punishment".
There are fears that the ongoing rocket attacks could harm the peace talks between the Israelis and the West Bank-based government of Mahmoud Abbas, the Palestinian president.
Abbas has no effective control over Palestinians in the Gaza Strip after the Hamas movement took full control of the territory by forcing out security forces loyal to the president.