I've had only glass, but I hear great things about acrylic. The worst part about acrylic(other than the price) is that it scratches easliy. I love glass, and I don't think you have to worry too much about breakage if you get a quality one. If I was going for a large tank with an exotic setup (ie a centerpiece for a living room) I'd get acrylic. Otherwise glass makes a great aquarium.

Just take care when you're cleaning the acrylic tank. Like they make scrubby pads for algae removal for acrylic - don't make a mistake and pick up one that's NOT safe for acrylic.

But even with a three year old - are you afraid that s/he will knock it over?? Or tap on it so hard that it'll break?? I guess I'm thinking that even with a three year old, acrylic or glass isn't really that much of a factor. Just make sure any tank you get is in a place or a stand that will not tip, and explain to your little one that tapping will upset the fish.

Also what size tank are you looking at?

Acrylic is much more expensive and scratches easily. That said the safety factor probably is worth it.

My oldest acrylic tank is eighteen years old and has almost no scratches on it. When cleaning the tank it is far better to start at the surface and clean towards the bottom. If a piece of gravel gets stuck on the cleaning pad it will scratch the inside of the tank. I have a six year old son and a three year old grand daughter and neither tank has had any damage at all other than a streak of nail polish on one tank. I have just not got around to scraping it off.

I think acrylic taks look better. Many glass tanks have ugly trim. I like the look of clear acrylic all over.