These are some ideas I would use with my junior ASD class, with ages ranging from four to seven.
Lego addition: use Lego blocks for simple addition, instead of numbers. Visual and far more engaging for early number work!
Lego patterns- make sample pattern towers using different colours - the children can build up from two colours to three to four
Shape/number/ colour hunt- children can go on a number/ shape hunt around the classroom/ yard
Pass the ball- pass a ball from child to child and keep count aloud together . Then count backwards!
The singing walrus channel on YouTube do lots of great number songs, my class love them!
Topmarks have lots of excellent interactive games too which are great for early mathematical activities.
Simple measuring activities around the classroom- length , weight and capacity are fun ones!
Tie it in with sorting to sort tall and short pictures of animals, people etc.
Stick number stickers to corresponding Lego blocks.