Ok, so bit of background:
MIL is bipolar, and her condition has gotten increasingly more severe over the years . She is on numerous medication, and was also diagnosed with borderline schizophrenia last year. Her condition varies, though is reasonably well controlled in that she doesn't pose a threat to herself or others. She goes through periods where she is either completely 'normal' or very depressed. I can usually tell when she is the former cos we have no contact with her for weeks-I will call and leave her numerous messages (which she won't answer) or I will call round (she won't open). FIL looks after her, though they have had marriage troubles for years. DH has buried his head his head in the sand and refuses to accept there is a problem. I have to nag him to call his mum, which he reluctantly does, but I have given up doing this as I don't want to interfere in their relationship.
My concern is that as I work part-time, MIL comes round every week for a few hours to be with DC (18 months). She always does it at the same time (when I am not home), even when she's going through a depressive stage. The nanny is at home with DC, but the last few weeks she has had to leave early meaning DC has been left alone with MIL. Both times he has fallen and sustained an injury after she (the nanny) has left-not huge, but enough to bruise substantially. I casually asked her about them when I got home, but she said she couldn't remember how he got them. I realise being a boisterous boy, it could happen with anyone but I am starting to feel worried him about leaving him with her now. BAsically I want to ask MIL to come round (or we can go round) when I am at home, but she refuses to do that. She has been distancing herself from DH and I for a while now, and I genuinely don't know why. At the same time, I don't want to limit her seeing DS, or vice-versa cos DS ADORES her. He loves seeing her, and I don't feel it's fair or right for me to do this. But how can I voice my concerns without it seeming like I am accusing her of harming DS?
TIA