Think about it this way, if she's babysitting him solo outside of her/your home then she will have to pay him attention. Maybe discuss with MIL she can do with DS during the day of the wedding, are there any local attractions they can visit for example?

That said, I can understand why you might be apprehensive about spending a full day and night together if they don't have a close relationship. Is it possible for MIL to spend some time on her own with DS before the wedding? Maybe she would behave differently if you weren't there?

Ah that's a shame.

Perhaps she's a bit clueless on how to interact with children... Assume SIL/BIL aren't too happy that MIL sits on her phone with their DS either? Perhaps you could give some give some subtle hints/ideas on things to do to keep the children busy? Arm her with some toys, books, etc?

Do we have the same mil??

Constant complaining that she never has time with DD (age 2.5years) and it's not fair my parents see her so much more. My parents live 15 mins away and do a day per week childcare for us, she lives 2 hours away so it's not due to just being unfair to her. It's logistics!
My parents are on holiday so we arranged mil to come and do the childcare day which we had expected her to be pleased about because she's always saying how it's sad she doesn't get to come and see dd more and do things with her etc etc.
made it clear there was no obligation, if she felt she couldn't or didn't want to then no hard feelings and we would use holiday to cover the two days.

Last week she bought dd home from playgroup after literally ten minutes saying it wasn't a good playgroup (church hall dd usually really enjoys it) and sat her in front of tv for 2 hours.
I had arranged to wfh so I could help / answer questions if she needed but stayed out of the way so she didn't feel watched. Saw they were watching tv and had been for a while so suggested dd get some of her toys to play with - she did. Mil then sat on the sofa and didn't join in whilst dd played alone.
Dd then asked to go in her sandpit. Fine. Mil opened it up then sat on the garden bench on her phone.

Of course I'm grateful she came to help with childcare but I'm fed up that she complains about having less relationship with her and wants time with her if she's going to waste it / spend it not actually engaging with her when that's what she needs.

This week I've booked a range of activities and given her a clear plan of the day "soft play is booked for X-y time but she will prob only manage half an hour on her own so it's important to join in with her and ask her questions mil, then there's story time at the library on the way home..." etc.

I didn't want to micromanage it but I also don't want dd to be bored senseless or left in front of the tv / playing alone for 8 hours, especially when I said I'd take the time off to do the childcare myself!
I want them to build a relationship too though!

I feel your pain!

I think you need to do what will help you relax and enjoy the wedding.

Leaving your son with your mother will do that.

Bringing your MIL will have you concerned and worried if he doesn't settle.

A weekend away is precious.

As your MIL to do an evening babysitting etc.

I wouldn't risk it.

Think of YOUR enjoyment IMO.

Can you do a practise run and see how she manages after a couple of hours? Looking after toddlers is bloody hard work and if she's not used to it and he's not used to her then I don't think either will be happy.

Why do people keep saying she might not be used to young children? She’s had at least one of her own!

This sounds like my mum!! Totally disconnected from the kids but happily holds her arms out saying ‘come and give gran a cuddle’ - well it’s like a stranger asking for a cuddle in their eyes! I wouldn’t let my mum babysit because like your MIL she doesn’t concentrate and at 18 months you need eyes in the back of your head, so it would be a big fat no from me if I were you.

I’m one of 3 and it amazes me how bad my mum is with small kids. I have no idea how she raised 3 babies!

You’re not unreasonable to not feel comfortable with her babysitting for the day. But the problem is that she has already been asked. This is a communication problem between you and your DH more than anything else. Un-asking her would most likely cause a big drama.

if I was in your situation I would most likely go ahead with the plan, knowing that a few hours of intermittent attentiveness is not going to have a lasting impact on your DS if he needs are otherwise well met. Then you need to set your boundaries with your DH.

I'm one of those people 🙋🏻‍♀️

Depending on the age of DH/his siblings, it might well be 30+ years since MIL has had to interact with young children. Maybe she wasn't too great at it at the time!

Not everyone is a natural with young children, some people might need a bit of pointing in the right direction.

I understand OP, bedtime is tricky in our household too so would be a consideration in terms of babysitting if it went through to nighttime (naps too but our DS is younger).

In your shoes I would weigh up the needs of DS vs. the needs of MIL. If you really don't think DS will settle with MIL then it's not really fair on him, since it's a long day away from home with someone he's not used to spending a lot of time with. Assuming practice runs are out of the question (and clearly these practice runs need to involve MIL better engagong with DS) I think it's fair to say that now the wedding is getting closer you need to change plans.

Is it an option for your mum to stay at your home/her home with DS? Assuming DS is more used to either of those scenarios they might be a better option for the wedding and more easily explained to MIL. I don't think you can invite your mum instead of MIL to the wedding and it not be incredibly awkward.

You don't have to leave him, with anybody you don't want to leave him with?! Your his Mum!

You’ll be stressed and worried and baby will be crying all day. I would do what is best for you and baby - ask your mum. It will be awful for your son to spend the day distressed and he will always hold that against her.

Exactly what I was thinking!!