Start with Toy Safety Directive, then read the Low Voltage and RED Directives, then finally look at the RoHS and General Product safety Directives.
For each directive, there will be a tabulation of harmonized standards, among which you must find the scope statements that are applicable to your product.
I am not a lawyer, so cannot offer any useful advice on intellectual property, copyright, patent, or trademark mitigation issues.
Start-up 'culture' sucks, at least in North America. Much risk, poor ethics, and difficult financing make North America in general, and the U.S. in particular, a messy and wonderful and awful environment for start-ups.