T.G.
Each kid is different. I introduced the sippy cup to all my children at 6 months of age. I used plastic cups with lids for my kids until they were 3. The only time they used a cup without a lid or straw was if we were in the kitchen and there was only a sip or two in the cup. I did this to help make meal times easier for me since we have 4 children and I wanted to spend less time cleaning up milk spills and more time sitting and eating with the family! Using sippy cups or cups with lids and straws has had no ill effect on any of my children and has not led to any delay in hand eye coordination.