For having children: Children are a source of joy for everyone and lack of children is cause for unhappiness. The following are some time tested remedies.
1. Santana Gopala Mantra: Devakisutam Govindam Vasudevam Jagatpatim DehimeTanayam Krishna twam-aham Sharanagatah. Recite this preferably 108 times and worship Bala Gopal photo or idol with Tulasi leaves and akshantas if possible.
To have a son:
1. Sarvabadhabinirmukto dhanadhanyasutanvitah Manushyo tatprasaden bhavishyati na samshayah.
2. Om hrim lajja jjalyam thah thah lah om hrim svaha.
Reciting Bala Kanda from Ramayana is a highly recommended remedy.