You certainly wouldn't want to expose your baby to the dust, especially dust from a 104 yo house (asbestos, lead, etc.). I would stay with your SIL while the work is being done and before moving back in, have the house professionally cleaned top to bottom and especially, have your HVAC ducts cleaned, if any. DH and I stuffed old towels down into ours when we did our last remodel and we still ended up with a ton of dust in them.

From what I understand, there are "things" you can put over all of the vents in the house to seal them off so that construction dust can't get in them -- or at least has a much more difficult time getting in; but it is still advised to have your ducts professionally cleaned after the construction is done and before you used the HVAC system again.

I would also have an air quality test done before you and the baby move back into the house.

Presumably your contractors are RRP Certified, and lead abatement is part of the renovation. No way should you be there during that. If that isn’t on your plan, then you don’t have the right contractor!

Don’t risk it!