Do you need the amount for your son's school education or just a college education?
Assuming you need it for college. In that case, you will need the amount when your son is around 16 - 18 years old.
1. If you don't want to take any risk, you may open a monthly RD of Rs. 1000 in the post office or bank.
OR 2. If you can take a little risk, you may do a monthly SIP of Rs. 1000 in Index Mutual Funds.
Example:
Monthly SIP: Rs. 1000
Total amount invested in 15 years: 1000 x 12 (months) x 15 (years) = Rs. 1,80,000
Assuming an interest of 12% in Index funds,
Estimated returns: Rs. 3,24,576 Total value: Rs. 5,04,576 after 15 years
3. If you want to generate more amount than this, I'd suggest you increase the SIP amount every year by 100.
Then you'd invest
Rs. 1000 monthly in 1st year
Rs. 1100 monthly in 2nd year
Rs. 1200 monthly in 2nd year and so on. In that case, the total amount you will receive after 15 years would be around Rs. 8,00,000. In my opinion, this is the best investment plan for you.