Treasure chest - teams of 4-8 (up to 4 teams). Put all the discs 'treasure' in a central area 'the treasure chest'. Create 'islands' for each team 5-10m away from the centre (use compass points). Players line up on their 'island'. On 'go' the first player from each team runs to the centre, picks up a disc and attempts a pass back to the next person in the line on their team. If successful they keep the treasure, if not it must be returned to the 'chest'. Aim to get more treasure than the other teams. Reverse game to get the treasure back into the chest.
Piggy in the middle - children stand in a circle with one or two players in the middle. They pass the disc around the circle (they cannot throw to the person next to them) - the player(s) in the middle try to intercept.
Relay races - come up with any fun relay race that include throwing, catching, running, passing. Vary the aim - it could be speed or accuracy. Encourage friendly competition between groups.
'IT' - keep the disc away from the people / team that are 'it' - you can't run with the disc. Remember non-contact.
Frisbee naughts and crosses relay - naughts are upward-turned discs, crosses are downward-turned discs. 2 teams stand 5-10m away from the 'board' (hoops or cones). One player from each team runs in and places a disc in position, they run back and tag the next person. Once discs are placed allow players to turn a disc over instead of placing a new disc. Normal naughts and crosses rules apply.
Targets - aim for disc to land in or hit different targets (hoop, bucket, knock a bottle over)
Zig-zag cones - running or passing games between zig zag cones. Relay or team challenges.
Round the world - players are split into two teams and line up on the baseline of a court. One player from each side steps up to the baseline and makes a throw (preceded by a catch once the game has started). The player then runs to the back of the line on the opposite side.
Race to the endzone - two teams of 2 or more (depending on space) line up on one endzone line. They have to make passes (without travelling) until they reach the opposite endzone line. It's a race to see who gets there first. You could include penalties for drops (go back to start, take 2 steps backwards ...etc). Advanced option - teams can play defence on the other team as well as trying to get their own disc over the line first - requires min 3 players per team.
Hot box - square playing field with a small scoring box in the middle that both teams are trying to attack / defend. Normal Ultimate rules. Teams should make a pass backwards or get the disc outside the boundary line before trying to score. Vary space and rules for skill level.
Plenko - Two teams (any number of players). Two endzones (2m x 2m) at either end of the pitch. Two discs are in play (each team starts with one). Players can run with the disc. Once they cross the halfway line players can be "tackled" if they are tagged whilst holding the disc, resulting in a turnover. Players are allowed to pass the disc but if it is dropped in the opponents half it results in a turnover. A score is made by "touching down" the disc in an opponents end zone, or by throwing the disc so that it stops in the endzone. An additional rule is that "tackles" can be made by succesfully throwing and hitting an opponent in your own half.