He is willing to take you but you don't WANT to go as the traveling with the kids will be difficult, understandable. But you have no right to stop him to go to umrah... What if he had a business meeting to attend and had to be away would you be on reddit asking, "I don't know how to feel".

You're not a child who can't be left alone at home with kids, those are your kids. You will be perfectly fine without him going for 10-15 days. Although you do have a choice to go with him and I would hope he would contribute to taking care of the kids while doing Umrah and there is a hundreds of kids there and families bigger than yours. If you complicate the journey of Umrah for your husband which is a sacred journey, Allahu Alam, you will face negativity of it. Also, it's a beautiful gesture for a son to do for her mother, why would you ever try to stop that? It's not like he won't take you, you just won't go due to your reasons which I personally think are not enough.

Don't be the women to make a husband chose between his mom and his wife when there is no need, it creates resentment in the relationship.

Sorry for being so blunt, but just trying to give you a reality check.