I think you're going to struggle to find any worthwhile investments for that sum of money unless you're going to do individual stocks, or an ETF like @jbot mentioned.
Most decent mutual funds start at an initial $2500 investment, with better ones starting at $10,000, then $50,000, then $100,000+
It also depends on your risk tolerance, diversification strategy, timeline to withdrawl, etc. At $500 per kid -- you might just be better off in a CD.