Suitable for ages down to 5, running for two days is an unlikely combination, let alone being that long and not having loads of fiddly pieces. You’re probably best off picking something of an average duration then building some kind of campaign or tournament with it. Here are a few that might work:
King of Tokyo: pretty good fun and one of the games I’ve seen work best for adults and kids together.
Dixit: very accessible, though the ambiguous language it can require might mean younger players struggle.
Once Upon a Time: Group based storytelling game.
Saboteur: Excellent, sometimes shouty, simple map based card game. Can be hard to find despite having been printed by around a dozen publishers.
Of course, if you want something that runs for a long time, Risk Legacy is worth a look. Again, possibly a bit much for five year olds though.