State TV said the shelling just before noon caused widespread material damage to the town of Suqailabiyah. It said the dead also included a 35-year-old woman.
State news agency SANA said Syrian troops had retaliated by firing shells toward insurgents' positions on the southern edge of Idlib province, the last major rebel stronghold in the country. Al-Qaida-linked Hayat Tahrir al-Sham, or HTS, is the main insurgent group in the area.
Priest Maher Haddad told The Associated Press by telephone from Suqailabiyah that a rocket struck near a group of children, instantly killing five and wounding others. He said the woman was killed in a nearby street by a separate rocket.
"The kids went out to play after some days of calm," Haddad said, since the town had not targeted for days by insurgents who were pushed further north by the Syrian army.
The Britain-based Syrian Observatory for Human Rights, an opposition war monitor, also reported that six people were killed, adding that eight others, including six children were wounded.
The Observatory said government shelling of a rebel-held village to the north killed one person and wounded others.
The insurgent enclave has been rocked by a wave of violence since April 30, killing and wounding dozens while forcing some 150,000 people to flee their homes in rebel-held areas. Idlib is home to some 3 million people, many of them displaced from other parts of the country.
Syrian troops have been on the offensive under the cover of airstrikes for days, capturing several strategic locations and villages.
Turkey's official Anadolu news agency on Sunday reported Turkish military deployments in southeastern Kilis province and southern Hatay province, both bordering Syria. The fresh commando and armored vehicle deployments were to reinforce border units, according to the agency.
The Observatory said that since the latest wave of violence began late last month 297 people have been killed.
Mroue reported from Beirut.