My DD was 14 months old when my Grandfather died, and we lived almost 500 miles away from him. Plus, at the time, I didn't drive. My XP (who did drive) refused point blank to attend the funeral, said that he'd only met "the man" a couple of times (which was true, but when they did meet, they seemed to get on brilliantly, and XP never had a bad thing to say about him), and announced that DD and I would have to drive up with my parents... whom I don't have a particularly great relationship with at the best of times.
I was the only family member there, without the support of a partner. And yes; I had DD to occupy me during the 3 days we ended up stopping (with my Grandmother, who was not only grieving, but furiously angry - and didn't care who knew it - with her daughter, my mother, at the time, for not having been there when my Grandfather died - which he did suddenly and, like your DH's Gran, in his sleep - so particularly awful and very awkward), but I felt so alone. I and my older brothers were very close to my Grandfather, and spent a lot of time with him whilst we were growing up... and, actually, he intuited that I was pregnant with DD before I even thought it a possibility... but they had their other halves there to support them in their grief, my parents had each other, my Grandmother had everyone's support, and I had... a 14 month old toddler who didn't understand what was going on. She was ridiculously good during the service and afterwards, but I do regret that she was there, in one way. Funerals aren't places for young toddlers. But XP refused to look after her, by himself, so... I was stuck. And now, years later, when my family say "oh, wasn't this bit of your grandfather's funeral so touching...?", or "wasn't it brilliant how supported we all were?", I'm left thinking - nearly 19 years later, mind - "I have no idea, because I was more focused on my DD" and "I wasn't supported in the least bit, thanks!".
If you can get someone to look after your DS, OP, during the funeral service at least, then... my advice would be to do so. But support your DH. Funerals are lonely places.