I've got two dogs, a Lab who's nearly 4, and a Golden Retriever who's nearly 3. I've got three kids, 11, 8 and 7. I do understand what you're saying, iris, as I often feel pushed for time too, and feel guilty that my dogs don't get enough exercise. They do get out every day, usually for a long walk to school and back, and then a good run round the park/field too. They are both young though, and bositerous, and I can't help feeling that they need more exercise than that. I have thought about rehoming them, to someone who will give them loads of exercise, but I just can't do it, and I don't think they're getting that raw a deal with me. I think, if they were able to say what they wanted, they would choose to stay here, with a family they adore who give them as much exercise as they're able to, than be rehomed somewhere where they could run all day.
As hard as it sometimes is, mkae that extra effort, iris, get out more, even with your little one in the pushchair. You'll feel better for it (I'm not intending to be patronising.) You'll regret it if you rehome your dog. It is hard when the weather is like it has been lately, but the nicer weather is on it's way, and we'll all benefit then.