As a child of the 80/90's, I would often go with my dad from age of 10ish (landscape builder) of a weekend/during holidays, it's how I earnt my pocket money 😉 I'd barrow bricks to where he was working, take back/unload the waste, load/unload the truck - I was strong and a real grafter, and learnt a lot! Where I wasn't of use, I'd sit in his truck drawing, eating warm jam sandwiches and just people watching...the customers would sometimes invite me in to watch TV ("Stanger Danger" 😉 I always politely declined), ply me with biscuits, home baked cakes and juice 😋 saying that, I don't remember spending any time frolicking on diggers (that was at the yard!!) or speaking longer than it took for him to smoke a cigarette and throw an 'order' towards the 'lackies' and I 🙃 as I got older, I was tasked with admin and accounts 🤷♀️
We've had work done recently and due to illness, the guy brought his young girl who was tasked with following him where he went. My children would've struggled with her in the house (SN) but I showed her where the garden toys were, ferried snacks/drinks and guided to bathroom when needed (however, if the trader left my bathroom in a mess like I'm assuming yours did, I wouldn't allow him either!). The trader mostly kept busy to be fair and was appreciative.
Of course in 'my' day, there wasn't as much concern for health and safety 😉 digger-daycare should be in their own time, work not impacted and the child away from danger. Legally, not certain on technicalities but think difficulties arise if during term time (impacts on education) and whether the young person (depending on age) is employed/paid (child labour/regulations) 🤔 operating machinery is likely the bigger issue 🙈