In a nutshell, yes, slime is perfectly safe for most kids.
Besides Borax, the two most common activators used in slime making are liquid starch (Sta-Flo) which contains sodium tetraborate and saline solution which contains boric acid. So essentially the active ingredient in all these activators is the same.
Mix one part flour with one part of water (eg, 1 cup flour and 1 cup water, or 1/2 cup flour and 1/2 cup water) until you get a thick glue-like consistency. Add a bit more water if it’s too thick. Mix well with a spoon to get rid of all the lumps.
First, pour off any standing liquid starch. Then add clear glue approximately 1/4 cup at a time and stir. Once the slime starts holding together, you will need to knead it by hand. After adding glue and kneading for 2-3 minutes, it will be just like new!
how to make slime with flour and water only
how to make slime with flour and salt
how to make slime with water and salt
how to make slime without glue
how to make slime with flour and conditioner