We live on a lake and so we own the whole gamut of life jackets for kids. Safety is obviously a huge priority, so here are some of my recommendations of what we have liked. Of course, with any safety items make sure to do your own research and do what is best for your family and interests.
--> For an infant or toddler that is 8-30 lbs you want to ensure you have a Type II life vest that includes the extra neck support and promotes face up floating. This one is the most comfortable we have found that offers more of an open neck style so your little one isn't miserable wearing it. Linked here.
--> Stearns Classic Life Vest is a good option for kids 30-50 lbs. It includes the extra security of a leg strap and us US Coast Guard approved. Linked here.
-->I have posted this before, but our favorite puddle jumper is the Body Glove Puddle Jumper. The build in vest is key so it doesn't slide off your little one and it comes in kid-friendly designs so they actually enjoy wearing it (again get over the fact it has obnoxious characters on it, my son is obsessed with putting on his "Dinoooo" vest). Linked here.