Putting a SW tank in a baby's room is a great idea, the soothing effects it can have is priceless. My youngest is 5 months old, and she would sit in her bumbo chair and stare at the big tank for hours if we let her. Both my older son's had tanks in their rooms when they were babies, and as such I'll soon be doing one for the little one.....I swore to the wife that the tank is just for her!
Don't worry about a tank tipping over, flooding or electrocuting anyone, just setup the system such that any of the noted conditions don't exist. Use a strong stand, keep the plumbing simple or don't have any at all, and practice good cable management and you'll be fine.