Hi C.,
I also have a 3.5 year old and am exclusively pumping for my 8 week old because of being unable to breastfeed. At around 6.5 weeks, I dropped from 7 pumps a day to 6 pumps a day by spreading out my time between pumps. My supply stayed the same. I plan to drop to 5 pumps in another week or so and then down to 4 a couple weeks later. Once you feel your supply is established, you can experiment with dropping pumps to see how it is affected. Most moms can't stay sane with a 7-8 times a day pumping schedule, but it is important early on!
I actually involve my 3.5 year old in the pumping process. He will help me get my supplies and will even get the baby his pacifier if the baby starts crying when pumping. If the baby is content, I will verbally play with my 3.5 year old (let's do the ABCs, Numbers, I-spy, etc.). If the baby is not asleep, I put him in his Ocean Wonders bouncy seat. There have been a few times where he is crying, but I try to keep pumping knowing that the breastmilk is for his own good. I also have a hands free bra that I use sometimes in a pinch. I can use the hands free bra and then lay my son on his boppy pillow and feed him. I only pump for 20 minutes at a time, so we can usually get through it.
There is a great community on iVillage for moms who are exlusively pumping. It has really helped me. http://messageboards.ivillage.com/iv-ppexcluspump
Also, once my son started sleeping through the night more (around 4-5 weeks), I stopped getting up at night to pump. I typcially go 7-8 hours at night without pumping. I get engorged, but am able to take care of it at the first morning pump.
If I can be of more assistance, feel free to email me.
J.