p.1 #2 · If you had to take pictures of a little kid birthday party inside
I know what i would take because it is what i have to use :
5D+35L+Flash
Kids in a party will let you get up close and smile for you. You will want them to know they are being photographed.
Candid pictures are not so cool in kids. Interaction is the key.
Some will say to use the 24-70 but i don't own one
If the light indoors is decent (usually is) you can get by without flash ( i use the 35 at f1.4-f1.8 at ISO 1600)
p.1 #4 · If you had to take pictures of a little kid birthday party inside
Any full frame body, plus Zeiss 21 f/2.8. Reason being that manual focus is easy because it's wide—so you don't miss focus much. And it's wide, so you get maximum kid action into the pictures, plus great image quality. Probably no need for flash, which means a great cake and candles. Shoot at ISO 3200 and you will get much better than 1/20th most anywhere. And for birthday party images, the full frame body allows size reduction that wipes out noise. The fast Canon wide primes would give similar results, but two stops faster.
p.1 #9 · If you had to take pictures of a little kid birthday party inside
The three f/2.8 zoom cover most events pretty well. The 35/1.4 and 85/1.2 are also handy in low light, but the 85 is a little slow for kids running around indoors. I shoot with 2 full frame bodies so I believe the 24/1.4, 17-55/2.8, and 50/1.4 are good choices on the 1.6x bodies, the 24 and 17-55 are probably over your budget now.
24-70mm @ 55mm
70-200mm @ 200mm
24-70mm @ 70mm (not a birthday party, christening)
p.1 #12 · If you had to take pictures of a little kid birthday party inside
I'm a fan of the Tamron 28-75 f/2.8. Very good optical performance (build is a bit weak but not too bad) and very good price and pretty good used market for them.
I picked mine up for $250 here at B&S (usually goes for around $300 or so last I checked) and works great.
Great event range on crop and good normal range on FF. AF is pretty good with my 5D's motor - unsure how it would perform, AF-wise, on 60D.
p.1 #18 · If you had to take pictures of a little kid birthday party inside
I use a 1d3, 24-70L and a 580 flash...because that's what I have. sometimes bounced, sometimes direct with -ve FEC to take the edge off, but for kids parties you want wide. If you're dealing with 1.6 crop, you'll want < 20mm so a Canon 17-55 f2.8 IS would be a nice choice.
Sell it when you finally get a FF, you won't lose much.