I most often say yes, we pretty much have an open door policy at our house. I have a house full as it is, (6 kids) but I'm always being asked to watch one (Or 4/5) out of my 10 nieces/nephews, along with my friends & acquaintances kids, & yes even total strangers. I really don't mind, 1 more play mate for my kids, & if they don't get along well with each other I use it as a good patience/communication lesson for my kids. If it's an actual true emergency I'm usually always there to help, pretty much no matter what I'm doing or where I'm at I'll drop what I'm doing to help. If the persons just in a tight spot, like everyday babysitter got sick at the last Min. & M. just cannot afford to take another sick day, then I make a nice point of letting them know this can't be a super regular/take advantage thing but will totally help if I can. As far as sickness goes, life just doesn't stop because my kid(s) get sick. If the other kid is sick I really don't mind them coming over as long as their not puking their guts out or have meningitis or something of the sorts LoL I'm always watching kids with green snoggy noses, sneezes /coughs, the works. I'm majorly into the Natural healing/ natural preventative health, so my kids have pretty darn strong immune systems, & if they catch the common cold or flues from a kid I just figure it par for the course, I don't get upset or curse the M. for sending a sick kid to my house. If anything it's just one more way to build their immunity against the common sicknesses they'll come across at the park or grocery store anyways. I think it's because of that, that my kids hardly get sick, & when they do it's usually in it's mildest form.
That's just me tho, you shouldn't feel pressured or obligated to say yes. Nor should you feel bad for saying no. The sick kids thing is different since your husband is disabled. About the money thing, I don't accept money from my brother's/sisters, or my closest closest friends. BUT I do expect them to help me when I need it. Also If it's a TRUE emergency, like last week a M. in my daughters class that I've met once, unexpededly wound up in the hospital for 2 weeks. Grandma couldn't fly in till the 5th day & dad had to work then visit M. after work, so dad remembering that I do foster care called an aquaintance we have in common who has my number, she called me & I picked the kids up an hour later. The grandma tried to pay me when she got here, but I refused. BUT in the case of babysitter called in sick M. can't afford to take a sick day, you bet I'll take the money! Lol If she offers it to me that is, I wouldn't force the issue of payment if it was a one time thing, but if babysitter is out sick all week then yeah I'd ask to be paid.