How long can visitors stay at a stretch?

[ShuchiC]

My parents will be visiting me this year, and I would like them to stay a little over six months, may be seven months. Is there a limit on how long they can stay (without applying for extensions)? They already have their visitor visas, and visited once, more than a year ago, when they only stayed for about one month. I would like them to stay longer this time as we will be having a baby. Thanks!

Edit: they currently have 10 year multiple entry visa, with several years left before expiration.

[ramabalaji]

Your parent stay in USA depends on the answers they give to IO at POE. The maximum stay granted in 6 months which will be stamped in their I 94 card. They need to leave USA on or before that date.
If they want to stay over and above I 94 date, they need to apply for an extension with a valid reason.