Hi, so sorry to hear about your daughter. My wife was diagnosed with acute myloid leukemia in July 2024 and we have 2 kids, the youngest was 21 months at diagnosis so similar ages. She was 33yrs old. It's a horrendous shock and every cancer journey is different. I can't give any advice about breast cancer treatment. I hope her treatment is fairly planned, if you have appts and a schedule of whats happening when that'll be really useful so you can concentrate your help at times they most need it. My wife ended up being in hospital for 3 of the past 6 months between admissions for aggressive chemo and sepsis due to neutropenia but that's more because her immune system was wiped for her type of cancer, I wouldn't expect that with breast cancer. 

Obviously because of my experience I massively sympathise with her partner, it has honestly been the most horrendous time worrying about her, and trying to keep the kids stability as much as possible, keep the house going, supporting her to keep going physically and mentally. So make sure her partner has some time out to just go on a walk, meet friends and do some normal stuff. I reisted because I felt I wouldn't be fulfilling my role of looking after everyone but it just meant I was more burnt out which doesn't then help anyone.

For the kids, stability is key, try to stick to routine as much as possible. It's so dependent on each child and their nature but I have a very energetic youngest son and his behaviour went off the charts when lots of different people were helping/putting him to bed (although my wife had just disappeared into hospital for 5 weeks unexpectedly so that certainly added to how unsettled he was). So when you're helping it may be you can do bedtimes etc or it might be that actually bedtimes by the parents while you help tidy up after tea is the best help. If you're staying overnight and the wee one is up at night time, just ask what they want you to do in advance. Again they may love having a help for a night time wake or they may say leave it to us and if you get up in the morning with them that'd be great. So just ask what's helpful and that may change as things go and you all get used to a new groove with you staying occasionally. 

Don't underestimate how mentally draining it will be over time. I've definitely felt overwhelmed when with my youngest, especially as he turned 2 and became even more energetic and makes alot of noise. It can be a challenge when you have no bandwidth left, so your daughter and her partner may absolutely love having the distraction but at times just be totally overwhelmed/overstimulated with the wee one. Again depends on how crazy or chill ur grandchild is .

Thankfully my wife is in remission and we are in the 2 weeks after finishing treatment but she is exhausted and we're both processing the insanity of the past 7 months. We naively thought we'd be able to get back to normal quickly but with her physical recovery likely taking months and both of us mentally exhausted we're still needing help with the kids. So worthwhile remembering when she's done treatment t that they might crash and burn depending on how crazy their journey has been so help may still be appreciated.

I wouldn't have got through the last 7 months without my parents and in laws support. They were fantastic and helped with the kids so much and I'll be forever grateful that a horrendous time was made easier by their support and meant the kids got through as best as they could as well.

Best of luck to you all

Thank you so  much for your helpful reply and very glad to hear your wife is through her treatment    Really useful tips and will bear them in mind. 
very best wishes to you and your family 

Thank you so  much for your helpful reply and very glad to hear your wife is through her treatment    Really useful tips and will bear them in mind. 
very best wishes to you and your family