Today while we were visiting she brought out this dusty dirty wagon filled with blocks, legos which were also covered with dust and dog hair

I cringed as I watched my 4 year old play with the toys but didn't want to be rude. I would NOT let DD get down on the floor to play which she was super pissed about because I knew she would put all that disgusting mess in her mouth

Talked to Dh about it on the way home and he said he was super disgusted by it too. WWYD about this? We dont want to be rude but it's seriously gross. She is the nicest lady btw, and I just adore her besides this.
Snuggling after a nap!
Claira 2 yrs and Sophia 11 months

Re: MIL your house is filthy :(
as soon as she brings it out i'd just say "oh let me wash all that stuff off for you, dust builds up quick on unused stuff, huh?" that way it gives her an out, she doesn't need to look like she was going to let them play with it as-is and you look like you're helping her and being nice.
or bring your own toys and a blanket for the baby to sit on.
that being said, i wouldn't worry too much about it unless her home is filth, like not dirt, but like moldy. a little dog hair and dust never hurt anyone unless they're allergic haha, it's hard to not to cringe but i remind myself that my cringing is in MY HEAD, not an actual physical threat to my kid.