My kids are 8 and 4. I have an attitude of encouraging their curiosity and desire to learn, and to do my best not to push them too far.
With brewing, if they want to help with grain or the like, I give them something that they are capable of - for my 4 year old, that may just be carrying the specialty grain containers to the scale and pouring some in. For the 8 year old, it could be more of the bulk grain and stirring the mash after I've started it.
They both like wort since it is sweet too.
They will sometimes come down to the garage and just sit with me while I wait for things. My 4 year old also like to throw as much stuff as he can into my bucket of starsan, and also likes to go through my kegging toolbox which is on the floor in the basement room.
I let them do as much as they can and are interested in doing, and then they can go back upstairs if they want, or we can hang out. I ask the 8 year old if she wants to understand more, and if she has specific questions, we go through those details, but then if she gets bored, I just let her move on.
I do the same with woodworking. I started her on the lathe when she was 5, but she wasn't all that interested, and didn't get back on the lathe for over a year, and since then we have done a scattering of turning projects. I let her set the pace though, as I want it to be something that she wants to do, and not something that I force on her just because I think it is great.