three_bounce.dart

import 'dart:math' as math show sin, pi;
import 'package:flutter/animation.dart';
import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: ThreeBounce(
            color: Colors.red,
          ),
        ),
      ),
    );
  }
}

class ThreeBounce extends StatefulWidget {
  const ThreeBounce({
    this.color,
    this.size = 50.0,
    this.itemBuilder,
    this.duration = const Duration(milliseconds: 1400),
    this.controller,
  }) : assert(
            !(itemBuilder is IndexedWidgetBuilder && color is Color) &&
                !(itemBuilder == null && color == null),
            'You should specify either a itemBuilder or a color');

  final Color color;
  final double size;
  final IndexedWidgetBuilder itemBuilder;
  final Duration duration;
  final AnimationController controller;

  @override
  _ThreeBounceState createState() => _ThreeBounceState();
}

class _ThreeBounceState extends State<ThreeBounce>
    with SingleTickerProviderStateMixin {
  AnimationController _controller;

  @override
  void initState() {
    super.initState();

    _controller = (widget.controller ??
        AnimationController(vsync: this, duration: widget.duration))
      ..repeat();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: SizedBox.fromSize(
        size: Size(widget.size * 2, widget.size),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: List.generate(3, (i) {
            return ScaleTransition(
              scale: DelayTween(begin: 0.0, end: 1.0, delay: i * .2)
                  .animate(_controller),
              child: SizedBox.fromSize(
                  size: Size.square(widget.size * 0.5), child: _itemBuilder(i)),
            );
          }),
        ),
      ),
    );
  }

  Widget _itemBuilder(int index) => widget.itemBuilder != null
      ? widget.itemBuilder(context, index)
      : DecoratedBox(
          decoration:
              BoxDecoration(color: widget.color, shape: BoxShape.circle));
}

class DelayTween extends Tween<double> {
  DelayTween({double begin, double end, @required this.delay})
      : super(begin: begin, end: end);

  final double delay;

  @override
  double lerp(double t) =>
      super.lerp((math.sin((t - delay) * 2 * math.pi) + 1) / 2);

  @override
  double evaluate(Animation<double> animation) => lerp(animation.value);
}

You solved my problem today.
Thank you very much.