The Marauders and Lily travel back in time to Harry's fourth year and meet their kids and their friends. How will Harry react or will he find out?
GO THROUGH EDITING BY MY FRIEND
Back in time would be the past. This is the future for them. They would have went forward in time.
and in that moments james potter started to fangirl like crazy
After the year there should be a comma not a full stop, though because there is a full stop the 'he' should have a capital 'h'