assume you can bring your children, trouser suit fine or as welshcake said, if its different 'rooms' segregated be prepared that you might not see your DH till the end! but it might be half the room men and half the room women type segregation, and you could just seat yourselves somewhere in the middle on the room.
most muslim weddings will start very late, so dont get there on the dot else you'll be sitting around and 2 hours later the room might still not be half full! children very welcome at most weddings. how long the wedding lasts depends on the culture of wedding couple - and in most muslim cultures, the bride and groom expect that many guests will come who they wont necessarily know. sometimes its a colleague/friend/acquaintance of the parents, sometimes it might just be the neighbour/cousin/visitor of one of the invited guests coming along for the food and party!
as for 'no boxed gifts please' heres an explanation...
giving a card and money is more typical but as most muslim cultures are guess cultures they will not ask outright instead hint it by saying 'no boxed gifts please'. or 'we are moving house so we kindly request no boxed gifts'. but you could give a gift and put it in a gift bag instead of a box! hope that helps, and that you have a good time OP!
I second what Welshcake said. Be prepared not to see your DH while you are there, men and women are segregated. I have been.to two.Muslim weddings. At one I was treated as! honourary man. Shame, the women were having much more fun!