Hi
Sorry your mat leave/time with your baby is being 'soured' by work. I am guessing you are very conscientious & good at what you do, so they are naturally just coming to you.
As flowery suggests go to your line manager. It is their responsibility to a) manage your cover/workload and b) manage the rest of the team to not contact you.
Just be clear that you were happy to help with their queries initially, but you would like to be left alone now to focus on the baby. A proper break will ensure you are back ready for work when the time comes!
In the meantime if colleagues coming asking for help, I'd start to "train" them not to expect an immediate response. They will soon find out it is easier/quicker to find the solution themselves ask somebody still at work than bother you. You are not under any obligation to help them.
As for your helpful colleagues that are suggesting how wonderful your cover is....It could be that they think you are interested in knowing how they are getting on or it could be something less charitable. Whatever their reasoning or the reality there is little you can do about it at home. So try to ignore what they are saying.
Many covers want to be covers and aren't actually angling to take over the role.
Going on mat leave is one of the weirdest thing I ever did. You are still 'engaged' with the organisation, but you aren't there. There is somebody else 'being you' and you are at home dealing with a new baby which is whole new world and not all of it is nice/happy etc.
So easy for me to say (as this is your job/life!), but take your mat leave, enjoy time with your baby and return to work as planned. Work will still be there. You could rush back only to find that actually it is all ok and that they could have managed without you.
I write all of this as somebody similar to you. I had the calls, the comments about my cover etc. In the end I realised that work would carry on and switched my focus to the baby. The 6/9/12 months will fly by. You have years to work...
Good luck.