My opinion on the weight loss is to eat healthy, exercise and you will lose some of it before you meet. I wouldn't try to lose that much that rapidly but if you lose 15-20 lbs., you will feel better and will be in smaller size clothing.
I do have one other comment. I don't recommend taking your child on your first date or even the first few dates. As a social worker, I've seen way too many kids who had people come and go from their lives and seen the attachment issues involved. I suggest hiring a sitter or finding a family member to watch the child. That way, you can enjoy your date and get to know this man in person. If it develops into a long-term relationship, then it's time to introduce him to your child.
Meeting people online is great but they are not always what they appear to be. Just like a used car ad may look really good in the paper but when you actually see & test drive it, you find out it is not the right car for you.

In other words, he may have also misrepresented some facts about himself.