cooking is excellent, or making something each but as a group together.
limit the 'tools' to just one of each type so they have to wait their turn, take turns, request tools from each other.
depending on ability they can each earn tokens for requests and/or tokens for commenting on each others work.
A request will be 'I want spoon' or 'pass the bowl', a comment would be 'you're using all the sugar' or 'that's a triangle'.
Be particularly careful about your own language. Slow and clear and if you have to repeat, repeat exactly as you did before, but with visual prompts. So if you say 'put the spoon in the bowl', and it wasn't understood, you would then do it by modelling putting the spoon in the bowl and then taking it out for them to do it.
If a child hasn't understood something, provided they are engaged and listened then leave a gap about twice as long as you would normally for them to respond before you repeat.
Encourage their communication by acting stupid. If they say to you 'pass me the spoon' then (provided they can discriminate and are confident they used the right word, give them a fork).
Ask them what they think they might need to do next and various points and when one responds ask another what the first one said and if said correctly they get a token, or a go at cutting out a dough shape next or whatever it is you are using to reinforce their engagement and behaviours.