Maybe some nice sensory bags to start the lesson, if the objective is counting to ten (and beyond for your higher ability) then you can have collections of ten in lots of different ways. Eg, 10 cotton wool balls, 10 beads to thread, 10 pennies to plink into a jar, 10 feathers, 10 pieces of shiny paper, well you get the idea?
Whole group activity would be something like ten green bottles with lots of participation, then with the small groups maybe build in other elements of the curriculum EG using language to describe the textures, developing fine motor skills.
Your HA could move on to simple addition, matching digits to a set or counting in the teens.
Your lowers could be practising their 1-1 correspondence by picking up and transferring the objects as they count or, if you have space, by being a bit more physical EG beanbags through a hoop, hats on heads, teddies in chairs, bricks on a tower.
The possibilities are endless really, check what equipment they'll have in class and what opportunity you'll have to prepare it before hand.
If you have little opportunity for using resources you can also count actions like claps, head pats, stamps.