he's only 18months so need to make something robust and super simple
I'd probably start with 22.5mm industrial product such as Allen-Bradley 800F range, it's tough and available in hose proof versions so when he spills stuff on it you can wash it down.
Yeah that's exactly the kind of thing that inspired it, (like thishttps://www.amazon.co.uk/Sntieecr-Electric-Educational-Montessori-Learning/dp/B082NW2H1K/ref=sr_1_41?keywords=Electronics+Kit+for+Kids&qid=1670673873&sr=8-41 but he's only 18months so need to make something robust and super simple, so I don't have to spend all my time holding him up so he can do the light switches!