Parents visa rejected at Mumbai

[Sarah]

My parents had applied at the Mumbai counsulate

-They have two children & both are in the US & working
- I realised that my Dad had entered only one sons name in the column no 37. of the DS-156 .He did that because there was no space for adding the additional info there.
-In the interview the lady asked him

1.How many sons you have ?
Ans - 2 sons

2.She asked - So is the second son in India ?
Ans- No ,both of them are in the US

3.She then looked at the Affidavit of support & then rejected the visa. under (214b)

Could you please advise me on the following .

1.Should they reapply immediately ?
2.Where are they supposed to enter the details of sons in DS-156
3.Is it very difficult for parents whose children (both) are in the US ,with no other sibiling in India to get a visit visa ?
Pls. advise

Thanks

[immihelp]

1. They can.
2. There is a question specifically for that on second page.
3. Not really. Many people get visa.